System Resource Management Using Time-Independent Scheduling

ABSTRACT

Ensuring the appropriate utilization of system resources using weighted workload based, time-independent scheduling, including: receiving an I/O request associated with an entity; determining whether an amount of system resources required to service the I/O request is greater than an amount of available system resources in a storage system; responsive to determining that the amount of system resources required to service the I/O request is greater than the amount of available system resources in the storage system: queueing the I/O request in an entity-specific queue for the entity; detecting that additional system resources in the storage system have become available; and issuing an I/O request from an entity-specific queue for an entity that has a highest priority, where a priority for each entity is determined based on the amount of I/O requests associated with the entity and a weighted proportion of resources designated for use by the entity.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation application for patent entitled to a filing dateand claiming the benefit of earlier-filed U.S. patent application Ser.No. 17/080,072, filed Oct. 26, 2020, herein incorporated by reference inits entirety, which is a continuation of U.S. Pat. No. 10,853,281,issued Dec. 1, 2020, which is a continuation of U.S. Pat. No.10,331,588, issued Jun. 25, 2019, which claims priority from U.S.Provisional Application No. 62/384,691, filed Sep. 7, 2016, and U.S.Provisional Application No. 62/516,988, filed Jun. 8, 2017.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A illustrates a first example system for data storage inaccordance with some implementations.

FIG. 1B illustrates a second example system for data storage inaccordance with some implementations.

FIG. 1C illustrates a third example system for data storage inaccordance with some implementations.

FIG. 1D illustrates a fourth example system for data storage inaccordance with some implementations.

FIG. 2A is a perspective view of a storage cluster with multiple storagenodes and internal storage coupled to each storage node to providenetwork attached storage, in accordance with some embodiments.

FIG. 2B is a block diagram showing an interconnect switch couplingmultiple storage nodes in accordance with some embodiments.

FIG. 2C is a multiple level block diagram, showing contents of a storagenode and contents of one of the non-volatile solid state storage unitsin accordance with some embodiments.

FIG. 2D shows a storage server environment, which uses embodiments ofthe storage nodes and storage units of some previous figures inaccordance with some embodiments.

FIG. 2E is a blade hardware block diagram, showing a control plane,compute and storage planes, and authorities interacting with underlyingphysical resources, in accordance with some embodiments.

FIG. 2F depicts elasticity software layers in blades of a storagecluster, in accordance with some embodiments.

FIG. 2G depicts authorities and storage resources in blades of a storagecluster, in accordance with some embodiments.

FIG. 3A sets forth a diagram of a storage system that is coupled fordata communications with a cloud services provider in accordance withsome embodiments of the present disclosure.

FIG. 3B sets forth a diagram of a storage system in accordance with someembodiments of the present disclosure.

FIG. 4 sets forth a flow chart illustrating an example method forensuring the appropriate utilization of system resources using weightedworkload based, time-independent scheduling according to embodiments ofthe present disclosure.

FIG. 5 sets forth a flow chart illustrating an additional example methodfor ensuring the appropriate utilization of system resources usingweighted workload based, time-independent scheduling according toembodiments of the present disclosure.

FIG. 6 sets forth a flow chart illustrating an additional example methodfor ensuring the appropriate utilization of system resources usingweighted workload based, time-independent scheduling according toembodiments of the present disclosure.

FIG. 7 sets forth a flow chart illustrating an additional example methodfor ensuring the appropriate utilization of system resources usingweighted workload based, time-independent scheduling according toembodiments of the present disclosure.

FIG. 8 sets forth a flow chart illustrating an additional example methodfor ensuring the appropriate utilization of system resources usingweighted workload based, time-independent scheduling according toembodiments of the present disclosure.

FIG. 9 sets forth a flow chart illustrating an additional example methodfor ensuring the appropriate utilization of system resources usingweighted workload based, time-independent scheduling according toembodiments of the present disclosure.

FIG. 10 sets forth a flow chart illustrating an additional examplemethod for ensuring the appropriate utilization of system resourcesusing weighted workload based, time-independent scheduling according toembodiments of the present disclosure.

FIG. 11 sets forth a flow chart illustrating an additional examplemethod for ensuring the appropriate utilization of system resourcesusing weighted workload based, time-independent scheduling according toembodiments of the present disclosure.

FIG. 12 sets forth a flow chart illustrating an additional examplemethod for ensuring the appropriate utilization of system resourcesusing weighted workload based, time-independent scheduling according toembodiments of the present disclosure.

FIG. 13 sets forth a flow chart illustrating an additional examplemethod for ensuring the appropriate utilization of system resourcesusing weighted workload based, time-independent scheduling according toembodiments of the present disclosure.

FIG. 14 sets forth a flow chart illustrating an additional examplemethod for ensuring the appropriate utilization of system resourcesusing weighted workload based, time-independent scheduling according toembodiments of the present disclosure.

DESCRIPTION OF EMBODIMENTS

Example methods, apparatuses, and products for ensuring the appropriateutilization of system resources using weighted workload based,time-independent scheduling in accordance with embodiments pf thepresent disclosure are described with reference to the accompanyingdrawings, beginning with FIG. 1A. FIG. 1A illustrates an example systemfor data storage, in accordance with some implementations. System 100(also referred to as “storage system” herein) includes numerous elementsfor purposes of illustration rather than limitation. It may be notedthat system 100 may include the same, more, or fewer elements configuredin the same or different manner in other implementations.

System 100 includes a number of computing devices 164A-B. Computingdevices (also referred to as “client devices” herein) may be embodied,for example, a server in a data center, a workstation, a personalcomputer, a notebook, or the like. Computing devices 164A-B may becoupled for data communications to one or more storage arrays 102A-Bthrough a storage area network (‘SAN’) 158 or a local area network(‘LAN’) 160.

The SAN 158 may be implemented with a variety of data communicationsfabrics, devices, and protocols. For example, the fabrics for SAN 158may include Fibre Channel, Ethernet, Infiniband, Serial Attached SmallComputer System Interface (‘SAS’), or the like. Data communicationsprotocols for use with SAN 158 may include Advanced TechnologyAttachment (‘ATA’), Fibre Channel Protocol, Small Computer SystemInterface (‘SCSI’), Internet Small Computer System Interface (‘iSCSI’),HyperSCSI, Non-Volatile Memory Express (‘NVMe’) over Fabrics, or thelike. It may be noted that SAN 158 is provided for illustration, ratherthan limitation. Other data communication couplings may be implementedbetween computing devices 164A-B and storage arrays 102A-B.

The LAN 160 may also be implemented with a variety of fabrics, devices,and protocols. For example, the fabrics for LAN 160 may include Ethernet(802.3), wireless (802.11), or the like. Data communication protocolsfor use in LAN 160 may include Transmission Control Protocol (‘TCP’),User Datagram Protocol (‘UDP’), Internet Protocol (‘IP’), HyperTextTransfer Protocol (‘HTTP’), Wireless Access Protocol (‘WAP’), HandheldDevice Transport Protocol (‘HDTP’), Session Initiation Protocol (‘SIP’),Real Time Protocol (‘RTP’), or the like.

Storage arrays 102A-B may provide persistent data storage for thecomputing devices 164A-B. Storage array 102A may be contained in achassis (not shown), and storage array 102B may be contained in anotherchassis (not shown), in implementations. Storage array 102A and 102B mayinclude one or more storage array controllers 110 (also referred to as“controller” herein). A storage array controller 110 may be embodied asa module of automated computing machinery comprising computer hardware,computer software, or a combination of computer hardware and software.In some implementations, the storage array controllers 110 may beconfigured to carry out various storage tasks. Storage tasks may includewriting data received from the computing devices 164A-B to storage array102A-B, erasing data from storage array 102A-B, retrieving data fromstorage array 102A-B and providing data to computing devices 164A-B,monitoring and reporting of disk utilization and performance, performingredundancy operations, such as Redundant Array of Independent Drives(RAID′) or RAID-like data redundancy operations, compressing data,encrypting data, and so forth.

Storage array controller 110 may be implemented in a variety of ways,including as a Field Programmable Gate Array (‘FPGA’), a ProgrammableLogic Chip (‘PLC’), an Application Specific Integrated Circuit (‘ASIC’),System-on-Chip (‘SOC’), or any computing device that includes discretecomponents such as a processing device, central processing unit,computer memory, or various adapters. Storage array controller 110 mayinclude, for example, a data communications adapter configured tosupport communications via the SAN 158 or LAN 160. In someimplementations, storage array controller 110 may be independentlycoupled to the LAN 160. In implementations, storage array controller 110may include an I/O controller or the like that couples the storage arraycontroller 110 for data communications, through a midplane (not shown),to a persistent storage resource 170A-B (also referred to as a “storageresource” herein). The persistent storage resource 170A-B main includeany number of storage drives 171A-F (also referred to as “storagedevices” herein) and any number of non-volatile Random Access Memory(‘NVRAM’) devices (not shown).

In some implementations, the NVRAM devices of a persistent storageresource 170A-B may be configured to receive, from the storage arraycontroller 110, data to be stored in the storage drives 171A-F. In someexamples, the data may originate from computing devices 164A-B. In someexamples, writing data to the NVRAM device may be carried out morequickly than directly writing data to the storage drive 171A-F. Inimplementations, the storage array controller 110 may be configured toutilize the NVRAM devices as a quickly accessible buffer for datadestined to be written to the storage drives 171A-F. Latency for writerequests using NVRAM devices as a buffer may be improved relative to asystem in which a storage array controller 110 writes data directly tothe storage drives 171A-F. In some implementations, the NVRAM devicesmay be implemented with computer memory in the form of high bandwidth,low latency RAM. The NVRAM device is referred to as “non-volatile”because the NVRAM device may receive or include a unique power sourcethat maintains the state of the RAM after main power loss to the NVRAMdevice. Such a power source may be a battery, one or more capacitors, orthe like. In response to a power loss, the NVRAM device may beconfigured to write the contents of the RAM to a persistent storage,such as the storage drives 171A-F.

In implementations, storage drive 171A-F may refer to any deviceconfigured to record data persistently, where “persistently” or“persistent” refers to a device's ability to maintain recorded dataafter loss of power. In some implementations, storage drive 171A-F maycorrespond to non-disk storage media. For example, the storage drive171A-F may be one or more solid-state drives (‘SSDs’), flash memorybased storage, any type of solid-state non-volatile memory, or any othertype of non-mechanical storage device. In other implementations, storagedrive 171A-F may include mechanical or spinning hard disk, such ashard-disk drives (‘HDD’).

In some implementations, the storage array controllers 110 may beconfigured for offloading device management responsibilities fromstorage drive 171A-F in storage array 102A-B. For example, storage arraycontrollers 110 may manage control information that may describe thestate of one or more memory blocks in the storage drives 171A-F. Thecontrol information may indicate, for example, that a particular memoryblock has failed and should no longer be written to, that a particularmemory block contains boot code for a storage array controller 110, thenumber of program-erase (PIE′) cycles that have been performed on aparticular memory block, the age of data stored in a particular memoryblock, the type of data that is stored in a particular memory block, andso forth. In some implementations, the control information may be storedwith an associated memory block as metadata. In other implementations,the control information for the storage drives 171A-F may be stored inone or more particular memory blocks of the storage drives 171A-F thatare selected by the storage array controller 110. The selected memoryblocks may be tagged with an identifier indicating that the selectedmemory block contains control information. The identifier may beutilized by the storage array controllers 110 in conjunction withstorage drives 171A-F to quickly identify the memory blocks that containcontrol information. For example, the storage controllers 110 may issuea command to locate memory blocks that contain control information. Itmay be noted that control information may be so large that parts of thecontrol information may be stored in multiple locations, that thecontrol information may be stored in multiple locations for purposes ofredundancy, for example, or that the control information may otherwisebe distributed across multiple memory blocks in the storage drive171A-F.

In implementations, storage array controllers 110 may offload devicemanagement responsibilities from storage drives 171A-F of storage array102A-B by retrieving, from the storage drives 171A-F, controlinformation describing the state of one or more memory blocks in thestorage drives 171A-F. Retrieving the control information from thestorage drives 171A-F may be carried out, for example, by the storagearray controller 110 querying the storage drives 171A-F for the locationof control information for a particular storage drive 171A-F. Thestorage drives 171A-F may be configured to execute instructions thatenable the storage drive 171A-F to identify the location of the controlinformation. The instructions may be executed by a controller (notshown) associated with or otherwise located on the storage drive 171A-Fand may cause the storage drive 171A-F to scan a portion of each memoryblock to identify the memory blocks that store control information forthe storage drives 171A-F. The storage drives 171A-F may respond bysending a response message to the storage array controller 110 thatincludes the location of control information for the storage drive171A-F. Responsive to receiving the response message, storage arraycontrollers 110 may issue a request to read data stored at the addressassociated with the location of control information for the storagedrives 171A-F.

In other implementations, the storage array controllers 110 may furtheroffload device management responsibilities from storage drives 171A-F byperforming, in response to receiving the control information, a storagedrive management operation. A storage drive management operation mayinclude, for example, an operation that is typically performed by thestorage drive 171A-F (e.g., the controller (not shown) associated with aparticular storage drive 171A-F). A storage drive management operationmay include, for example, ensuring that data is not written to failedmemory blocks within the storage drive 171A-F, ensuring that data iswritten to memory blocks within the storage drive 171A-F in such a waythat adequate wear leveling is achieved, and so forth.

In implementations, storage array 102A-B may implement two or morestorage array controllers 110. For example, storage array 102A mayinclude storage array controllers 110A and storage array controllers110B. At a given instance, a single storage array controller 110 (e.g.,storage array controller 110A) of a storage system 100 may be designatedwith primary status (also referred to as “primary controller” herein),and other storage array controllers 110 (e.g., storage array controller110A) may be designated with secondary status (also referred to as“secondary controller” herein). The primary controller may haveparticular rights, such as permission to alter data in persistentstorage resource 170A-B (e.g., writing data to persistent storageresource 170A-B). At least some of the rights of the primary controllermay supersede the rights of the secondary controller. For instance, thesecondary controller may not have permission to alter data in persistentstorage resource 170A-B when the primary controller has the right. Thestatus of storage array controllers 110 may change. For example, storagearray controller 110A may be designated with secondary status, andstorage array controller 110B may be designated with primary status.

In some implementations, a primary controller, such as storage arraycontroller 110A, may serve as the primary controller for one or morestorage arrays 102A-B, and a second controller, such as storage arraycontroller 110B, may serve as the secondary controller for the one ormore storage arrays 102A-B. For example, storage array controller 110Amay be the primary controller for storage array 102A and storage array102B, and storage array controller 110B may be the secondary controllerfor storage array 102A and 102B. In some implementations, storage arraycontrollers 110C and 110D (also referred to as “storage processingmodules”) may neither have primary or secondary status. Storage arraycontrollers 110C and 110D, implemented as storage processing modules,may act as a communication interface between the primary and secondarycontrollers (e.g., storage array controllers 110A and 110B,respectively) and storage array 102B. For example, storage arraycontroller 110A of storage array 102A may send a write request, via SAN158, to storage array 102B. The write request may be received by bothstorage array controllers 110C and 110D of storage array 102B. Storagearray controllers 110C and 110D facilitate the communication, e.g., sendthe write request to the appropriate storage drive 171A-F. It may benoted that in some implementations storage processing modules may beused to increase the number of storage drives controlled by the primaryand secondary controllers.

In implementations, storage array controllers 110 are communicativelycoupled, via a midplane (not shown), to one or more storage drives171A-F and to one or more NVRAM devices (not shown) that are included aspart of a storage array 102A-B. The storage array controllers 110 may becoupled to the midplane via one or more data communication links and themidplane may be coupled to the storage drives 171A-F and the NVRAMdevices via one or more data communications links. The datacommunications links described herein are collectively illustrated bydata communications links 108A-D and may include a Peripheral ComponentInterconnect Express (‘PCIe’) bus, for example.

FIG. 1B illustrates an example system for data storage, in accordancewith some implementations. Storage array controller 101 illustrated inFIG. 1B may be similar to the storage array controllers 110 describedwith respect to FIG. 1A. In one example, storage array controller 101may be similar to storage array controller 110A or storage arraycontroller 110B. Storage array controller 101 includes numerous elementsfor purposes of illustration rather than limitation. It may be notedthat storage array controller 101 may include the same, more, or fewerelements configured in the same or different manner in otherimplementations. It may be noted that elements of FIG. 1A may beincluded below to help illustrate features of storage array controller101.

Storage array controller 101 may include one or more processing devices104 and random access memory (‘RAM’) 111. Processing device 104 (orcontroller 101) represents one or more general-purpose processingdevices such as a microprocessor, central processing unit, or the like.More particularly, the processing device 104 (or controller 101) may bea complex instruction set computing (‘CISC’) microprocessor, reducedinstruction set computing (‘RISC’) microprocessor, very long instructionword (‘VLIW’) microprocessor, or a processor implementing otherinstruction sets or processors implementing a combination of instructionsets. The processing device 104 (or controller 101) may also be one ormore special-purpose processing devices such as an application specificintegrated circuit (‘ASIC’), a field programmable gate array (‘FPGA’), adigital signal processor (‘DSP’), network processor, or the like.

The processing device 104 may be connected to the RAM 111 via a datacommunications link 106, which may be embodied as a high speed memorybus such as a Double-Data Rate 4 (‘DDR4’) bus. Stored in RAM 111 is anoperating system 112. In some implementations, instructions 113 arestored in RAM 111. Instructions 113 may include computer programinstructions for performing operations in in a direct-mapped flashstorage system. In one embodiment, a direct-mapped flash storage systemis one that addresses data blocks within flash drives directly andwithout an address translation performed by the storage controllers ofthe flash drives.

In implementations, storage array controller 101 includes one or morehost bus adapters 103A-C that are coupled to the processing device 104via a data communications link 105A-C. In implementations, host busadapters 103A-C may be computer hardware that connects a host system(e.g., the storage array controller) to other network and storagearrays. In some examples, host bus adapters 103A-C may be a FibreChannel adapter that enables the storage array controller 101 to connectto a SAN, an Ethernet adapter that enables the storage array controller101 to connect to a LAN, or the like. Host bus adapters 103A-C may becoupled to the processing device 104 via a data communications link105A-C such as, for example, a PCIe bus.

In implementations, storage array controller 101 may include a host busadapter 114 that is coupled to an expander 115. The expander 115 may beused to attach a host system to a larger number of storage drives. Theexpander 115 may, for example, be a SAS expander utilized to enable thehost bus adapter 114 to attach to storage drives in an implementationwhere the host bus adapter 114 is embodied as a SAS controller.

In implementations, storage array controller 101 may include a switch116 coupled to the processing device 104 via a data communications link109. The switch 116 may be a computer hardware device that can createmultiple endpoints out of a single endpoint, thereby enabling multipledevices to share a single endpoint. The switch 116 may, for example, bea PCIe switch that is coupled to a PCIe bus (e.g., data communicationslink 109) and presents multiple PCIe connection points to the midplane.

In implementations, storage array controller 101 includes a datacommunications link 107 for coupling the storage array controller 101 toother storage array controllers. In some examples, data communicationslink 107 may be a QuickPath Interconnect (QPI) interconnect.

A traditional storage system that uses traditional flash drives mayimplement a process across the flash drives that are part of thetraditional storage system. For example, a higher level process of thestorage system may initiate and control a process across the flashdrives. However, a flash drive of the traditional storage system mayinclude its own storage controller that also performs the process. Thus,for the traditional storage system, a higher level process (e.g.,initiated by the storage system) and a lower level process (e.g.,initiated by a storage controller of the storage system) may both beperformed.

To resolve various deficiencies of a traditional storage system,operations may be performed by higher level processes and not by thelower level processes. For example, the flash storage system may includeflash drives that do not include storage controllers that provide theprocess. Thus, the operating system of the flash storage system itselfmay initiate and control the process. This may be accomplished by adirect-mapped flash storage system that addresses data blocks within theflash drives directly and without an address translation performed bythe storage controllers of the flash drives.

The operating system of the flash storage system may identify andmaintain a list of allocation units across multiple flash drives of theflash storage system. The allocation units may be entire erase blocks ormultiple erase blocks. The operating system may maintain a map oraddress range that directly maps addresses to erase blocks of the flashdrives of the flash storage system.

Direct mapping to the erase blocks of the flash drives may be used torewrite data and erase data. For example, the operations may beperformed on one or more allocation units that include a first data anda second data where the first data is to be retained and the second datais no longer being used by the flash storage system. The operatingsystem may initiate the process to write the first data to new locationswithin other allocation units and erasing the second data and markingthe allocation units as being available for use for subsequent data.Thus, the process may only be performed by the higher level operatingsystem of the flash storage system without an additional lower levelprocess being performed by controllers of the flash drives.

Advantages of the process being performed only by the operating systemof the flash storage system include increased reliability of the flashdrives of the flash storage system as unnecessary or redundant writeoperations are not being performed during the process. One possiblepoint of novelty here is the concept of initiating and controlling theprocess at the operating system of the flash storage system. Inaddition, the process can be controlled by the operating system acrossmultiple flash drives. This is in contrast to the process beingperformed by a storage controller of a flash drive.

A storage system can consist of two storage array controllers that sharea set of drives for failover purposes, or it could consist of a singlestorage array controller that provides a storage service that utilizesmultiple drives, or it could consist of a distributed network of storagearray controllers each with some number of drives or some amount ofFlash storage where the storage array controllers in the networkcollaborate to provide a complete storage service and collaborate onvarious aspects of a storage service including storage allocation andgarbage collection.

FIG. 1C illustrates a third example system 117 for data storage inaccordance with some implementations. System 117 (also referred to as“storage system” herein) includes numerous elements for purposes ofillustration rather than limitation. It may be noted that system 117 mayinclude the same, more, or fewer elements configured in the same ordifferent manner in other implementations.

In one embodiment, system 117 includes a dual Peripheral ComponentInterconnect (PCP) flash storage device 118 with separately addressablefast write storage. System 117 may include a storage controller 119. Inone embodiment, storage controller 119 may be a CPU, ASIC, FPGA, or anyother circuitry that may implement control structures necessaryaccording to the present disclosure. In one embodiment, system 117includes flash memory devices (e.g., including flash memory devices 120a-n), operatively coupled to various channels of the storage devicecontroller 119. Flash memory devices 120 a-n, may be presented to thecontroller 119 as an addressable collection of Flash pages, eraseblocks, and/or control elements sufficient to allow the storage devicecontroller 119 to program and retrieve various aspects of the Flash. Inone embodiment, storage device controller 119 may perform operations onflash memory devices 120A-N including storing and retrieving datacontent of pages, arranging and erasing any blocks, tracking statisticsrelated to the use and reuse of Flash memory pages, erase blocks, andcells, tracking and predicting error codes and faults within the Flashmemory, controlling voltage levels associated with programming andretrieving contents of Flash cells, etc.

In one embodiment, system 117 may include RAM 121 to store separatelyaddressable fast-write data. In one embodiment, RAM 121 may be one ormore separate discrete devices. In another embodiment, RAM 121 may beintegrated into storage device controller 119 or multiple storage devicecontrollers. The RAM 121 may be utilized for other purposes as well,such as temporary program memory for a processing device (e.g., a CPU)in the storage device controller 119.

In one embodiment, system 119 may include a stored energy device 122,such as a rechargeable battery or a capacitor. Stored energy device 122may store energy sufficient to power the storage device controller 119,some amount of the RAM (e.g., RAM 121), and some amount of Flash memory(e.g., Flash memory 120 a-120 n) for sufficient time to write thecontents of RAM to Flash memory. In one embodiment, storage devicecontroller 119 may write the contents of RAM to Flash Memory if thestorage device controller detects loss of external power.

In one embodiment, system 117 includes two data communications links 123a, 123 b. In one embodiment, data communications links 123 a, 123 b maybe PCI interfaces. In another embodiment, data communications links 123a, 123 b may be based on other communications standards (e.g.,HyperTransport, InfiniBand, etc.). Data communications links 123 a, 123b may be based on non-volatile memory express (‘NVMe’) or NVMe overfabrics (‘NVMf’) specifications that allow external connection to thestorage device controller 119 from other components in the storagesystem 117. It should be noted that data communications links may beinterchangeably referred to herein as PCI buses for convenience.

System 117 may also include an external power source (not shown), whichmay be provided over one or both data communications links 123 a, 123 b,or which may be provided separately. An alternative embodiment includesa separate Flash memory (not shown) dedicated for use in storing thecontent of RAM 121. The storage device controller 119 may present alogical device over a PCI bus which may include an addressablefast-write logical device, or a distinct part of the logical addressspace of the storage device 118, which may be presented as PCI memory oras persistent storage. In one embodiment, operations to store into thedevice are directed into the RAM 121. On power failure, the storagedevice controller 119 may write stored content associated with theaddressable fast-write logical storage to Flash memory (e.g., Flashmemory 120 a-n) for long-term persistent storage.

In one embodiment, the logical device may include some presentation ofsome or all of the content of the Flash memory devices 120 a-n, wherethat presentation allows a storage system including a storage device 118(e.g., storage system 117) to directly address Flash memory pages anddirectly reprogram erase blocks from storage system components that areexternal to the storage device through the PCI bus. The presentation mayalso allow one or more of the external components to control andretrieve other aspects of the Flash memory including some or all of:tracking statistics related to use and reuse of Flash memory pages,erase blocks, and cells across all the Flash memory devices; trackingand predicting error codes and faults within and across the Flash memorydevices; controlling voltage levels associated with programming andretrieving contents of Flash cells; etc.

In one embodiment, the stored energy device 122 may be sufficient toensure completion of in-progress operations to the Flash memory devices107 a-120 n stored energy device 122 may power storage device controller119 and associated Flash memory devices (e.g., 120 a-n) for thoseoperations, as well as for the storing of fast-write RAM to Flashmemory. Stored energy device 122 may be used to store accumulatedstatistics and other parameters kept and tracked by the Flash memorydevices 120 a-n and/or the storage device controller 119. Separatecapacitors or stored energy devices (such as smaller capacitors near orembedded within the Flash memory devices themselves) may be used forsome or all of the operations described herein.

Various schemes may be used to track and optimize the life span of thestored energy component, such as adjusting voltage levels over time,partially discharging the storage energy device 122 to measurecorresponding discharge characteristics, etc. If the available energydecreases over time, the effective available capacity of the addressablefast-write storage may be decreased to ensure that it can be writtensafely based on the currently available stored energy.

FIG. 1D illustrates a third example system 124 for data storage inaccordance with some implementations. In one embodiment, system 124includes storage controllers 125 a, 125 b. In one embodiment, storagecontrollers 125 a, 125 b are operatively coupled to Dual PCI storagedevices 119 a, 119 b and 119 c, 119 d, respectively. Storage controllers125 a, 125 b may be operatively coupled (e.g., via a storage network130) to some number of host computers 127 a-n.

In one embodiment, two storage controllers (e.g., 125 a and 125 b)provide storage services, such as a SCS) block storage array, a fileserver, an object server, a database or data analytics service, etc. Thestorage controllers 125 a, 125 b may provide services through somenumber of network interfaces (e.g., 126 a-d) to host computers 127 a-noutside of the storage system 124. Storage controllers 125 a, 125 b mayprovide integrated services or an application entirely within thestorage system 124, forming a converged storage and compute system. Thestorage controllers 125 a, 125 b may utilize the fast write memorywithin or across storage devices 119 a-d to journal in progressoperations to ensure the operations are not lost on a power failure,storage controller removal, storage controller or storage systemshutdown, or some fault of one or more software or hardware componentswithin the storage system 124.

In one embodiment, controllers 125 a, 125 b operate as PCI masters toone or the other PCI buses 128 a, 128 b. In another embodiment, 128 aand 128 b may be based on other communications standards (e.g.,HyperTransport, InfiniBand, etc.). Other storage system embodiments mayoperate storage controllers 125 a, 125 b as multi-masters for both PCIbuses 128 a, 128 b. Alternately, a PCI/NVMe/NVMf switchinginfrastructure or fabric may connect multiple storage controllers. Somestorage system embodiments may allow storage devices to communicate witheach other directly rather than communicating only with storagecontrollers. In one embodiment, a storage device controller 119 a may beoperable under direction from a storage controller 125 a to synthesizeand transfer data to be stored into Flash memory devices from data thathas been stored in RAM (e.g., RAM 121 of FIG. 1C). For example, arecalculated version of RAM content may be transferred after a storagecontroller has determined that an operation has fully committed acrossthe storage system, or when fast-write memory on the device has reacheda certain used capacity, or after a certain amount of time, to ensureimprove safety of the data or to release addressable fast-write capacityfor reuse. This mechanism may be used, for example, to avoid a secondtransfer over a bus (e.g., 128 a, 128 b) from the storage controllers125 a, 125 b. In one embodiment, a recalculation may include compressingdata, attaching indexing or other metadata, combining multiple datasegments together, performing erasure code calculations, etc.

In one embodiment, under direction from a storage controller 125 a, 125b, a storage device controller 119 a, 119 b may be operable to calculateand transfer data to other storage devices from data stored in RAM(e.g., RAM 121 of FIG. 1C) without involvement of the storagecontrollers 125 a, 125 b. This operation may be used to mirror datastored in one controller 125 a to another controller 125 b, or it couldbe used to offload compression, data aggregation, and/or erasure codingcalculations and transfers to storage devices to reduce load on storagecontrollers or the storage controller interface 129 a, 129 b to the PCIbus 128 a, 128 b.

A storage device controller 119 may include mechanisms for implementinghigh availability primitives for use by other parts of a storage systemexternal to the Dual PCI storage device 118. For example, reservation orexclusion primitives may be provided so that, in a storage system withtwo storage controllers providing a highly available storage service,one storage controller may prevent the other storage controller fromaccessing or continuing to access the storage device. This could beused, for example, in cases where one controller detects that the othercontroller is not functioning properly or where the interconnect betweenthe two storage controllers may itself not be functioning properly.

In one embodiment, a storage system for use with Dual PCI direct mappedstorage devices with separately addressable fast write storage includessystems that manage erase blocks or groups of erase blocks as allocationunits for storing data on behalf of the storage service, or for storingmetadata (e.g., indexes, logs, etc.) associated with the storageservice, or for proper management of the storage system itself. Flashpages, which may be a few kilobytes in size, may be written as dataarrives or as the storage system is to persist data for long intervalsof time (e.g., above a defined threshold of time). To commit data morequickly, or to reduce the number of writes to the Flash memory devices,the storage controllers may first write data into the separatelyaddressable fast write storage on one more storage devices.

In one embodiment, the storage controllers 125 a, 125 b may initiate theuse of erase blocks within and across storage devices (e.g., 118) inaccordance with an age and expected remaining lifespan of the storagedevices, or based on other statistics. The storage controllers 125 a,125 b may initiate garbage collection and data migration data betweenstorage devices in accordance with pages that are no longer needed aswell as to manage Flash page and erase block lifespans and to manageoverall system performance.

In one embodiment, the storage system 124 may utilize mirroring and/orerasure coding schemes as part of storing data into addressable fastwrite storage and/or as part of writing data into allocation unitsassociated with erase blocks. Erasure codes may be used across storagedevices, as well as within erase blocks or allocation units, or withinand across Flash memory devices on a single storage device, to provideredundancy against single or multiple storage device failures or toprotect against internal corruptions of Flash memory pages resultingfrom Flash memory operations or from degradation of Flash memory cells.Mirroring and erasure coding at various levels may be used to recoverfrom multiple types of failures that occur separately or in combination.

The embodiments depicted with reference to FIGS. 2A-G illustrate astorage cluster that stores user data, such as user data originatingfrom one or more user or client systems or other sources external to thestorage cluster. The storage cluster distributes user data acrossstorage nodes housed within a chassis, or across multiple chassis, usingerasure coding and redundant copies of metadata. Erasure coding refersto a method of data protection or reconstruction in which data is storedacross a set of different locations, such as disks, storage nodes orgeographic locations. Flash memory is one type of solid-state memorythat may be integrated with the embodiments, although the embodimentsmay be extended to other types of solid-state memory or other storagemedium, including non-solid state memory. Control of storage locationsand workloads are distributed across the storage locations in aclustered peer-to-peer system. Tasks such as mediating communicationsbetween the various storage nodes, detecting when a storage node hasbecome unavailable, and balancing I/Os (inputs and outputs) across thevarious storage nodes, are all handled on a distributed basis. Data islaid out or distributed across multiple storage nodes in data fragmentsor stripes that support data recovery in some embodiments. Ownership ofdata can be reassigned within a cluster, independent of input and outputpatterns. This architecture described in more detail below allows astorage node in the cluster to fail, with the system remainingoperational, since the data can be reconstructed from other storagenodes and thus remain available for input and output operations. Invarious embodiments, a storage node may be referred to as a clusternode, a blade, or a server.

The storage cluster may be contained within a chassis, i.e., anenclosure housing one or more storage nodes. A mechanism to providepower to each storage node, such as a power distribution bus, and acommunication mechanism, such as a communication bus that enablescommunication between the storage nodes are included within the chassis.The storage cluster can run as an independent system in one locationaccording to some embodiments. In one embodiment, a chassis contains atleast two instances of both the power distribution and the communicationbus which may be enabled or disabled independently. The internalcommunication bus may be an Ethernet bus, however, other technologiessuch as PCIe, InfiniBand, and others, are equally suitable. The chassisprovides a port for an external communication bus for enablingcommunication between multiple chassis, directly or through a switch,and with client systems. The external communication may use a technologysuch as Ethernet, InfiniBand, Fibre Channel, etc. In some embodiments,the external communication bus uses different communication bustechnologies for inter-chassis and client communication. If a switch isdeployed within or between chassis, the switch may act as a translationbetween multiple protocols or technologies. When multiple chassis areconnected to define a storage cluster, the storage cluster may beaccessed by a client using either proprietary interfaces or standardinterfaces such as network file system (‘NFS’), common internet filesystem (‘CIFS’), small computer system interface (‘SCSI’) or hypertexttransfer protocol (‘HTTP’). Translation from the client protocol mayoccur at the switch, chassis external communication bus or within eachstorage node. In some embodiments, multiple chassis may be coupled orconnected to each other through an aggregator switch. A portion and/orall of the coupled or connected chassis may be designated as a storagecluster. As discussed above, each chassis can have multiple blades, eachblade has a media access control (‘MAC’) address, but the storagecluster is presented to an external network as having a single clusterIP address and a single MAC address in some embodiments.

Each storage node may be one or more storage servers and each storageserver is connected to one or more non-volatile solid state memoryunits, which may be referred to as storage units or storage devices. Oneembodiment includes a single storage server in each storage node andbetween one to eight non-volatile solid state memory units, however thisone example is not meant to be limiting. The storage server may includea processor, DRAM and interfaces for the internal communication bus andpower distribution for each of the power buses. Inside the storage node,the interfaces and storage unit share a communication bus, e.g., PCIExpress, in some embodiments. The non-volatile solid state memory unitsmay directly access the internal communication bus interface through astorage node communication bus, or request the storage node to accessthe bus interface. The non-volatile solid state memory unit contains anembedded CPU, solid state storage controller, and a quantity of solidstate mass storage, e.g., between 2-32 terabytes (‘TB’) in someembodiments. An embedded volatile storage medium, such as DRAM, and anenergy reserve apparatus are included in the non-volatile solid statememory unit. In some embodiments, the energy reserve apparatus is acapacitor, super-capacitor, or battery that enables transferring asubset of DRAM contents to a stable storage medium in the case of powerloss. In some embodiments, the non-volatile solid state memory unit isconstructed with a storage class memory, such as phase change ormagnetoresistive random access memory (‘MRAM’) that substitutes for DRAMand enables a reduced power hold-up apparatus.

One of many features of the storage nodes and non-volatile solid statestorage is the ability to proactively rebuild data in a storage cluster.The storage nodes and non-volatile solid state storage can determinewhen a storage node or non-volatile solid state storage in the storagecluster is unreachable, independent of whether there is an attempt toread data involving that storage node or non-volatile solid statestorage. The storage nodes and non-volatile solid state storage thencooperate to recover and rebuild the data in at least partially newlocations. This constitutes a proactive rebuild, in that the systemrebuilds data without waiting until the data is needed for a read accessinitiated from a client system employing the storage cluster. These andfurther details of the storage memory and operation thereof arediscussed below.

FIG. 2A is a perspective view of a storage cluster 161, with multiplestorage nodes 150 and internal solid-state memory coupled to eachstorage node to provide network attached storage or storage areanetwork, in accordance with some embodiments. A network attachedstorage, storage area network, or a storage cluster, or other storagememory, could include one or more storage clusters 161, each having oneor more storage nodes 150, in a flexible and reconfigurable arrangementof both the physical components and the amount of storage memoryprovided thereby. The storage cluster 161 is designed to fit in a rack,and one or more racks can be set up and populated as desired for thestorage memory. The storage cluster 161 has a chassis 138 havingmultiple slots 142. It should be appreciated that chassis 138 may bereferred to as a housing, enclosure, or rack unit. In one embodiment,the chassis 138 has fourteen slots 142, although other numbers of slotsare readily devised. For example, some embodiments have four slots,eight slots, sixteen slots, thirty-two slots, or other suitable numberof slots. Each slot 142 can accommodate one storage node 150 in someembodiments. Chassis 138 includes flaps 148 that can be utilized tomount the chassis 138 on a rack. Fans 144 provide air circulation forcooling of the storage nodes 150 and components thereof, although othercooling components could be used, or an embodiment could be devisedwithout cooling components. A switch fabric 146 couples storage nodes150 within chassis 138 together and to a network for communication tothe memory. In an embodiment depicted in herein, the slots 142 to theleft of the switch fabric 146 and fans 144 are shown occupied by storagenodes 150, while the slots 142 to the right of the switch fabric 146 andfans 144 are empty and available for insertion of storage node 150 forillustrative purposes. This configuration is one example, and one ormore storage nodes 150 could occupy the slots 142 in various furtherarrangements. The storage node arrangements need not be sequential oradjacent in some embodiments. Storage nodes 150 are hot pluggable,meaning that a storage node 150 can be inserted into a slot 142 in thechassis 138, or removed from a slot 142, without stopping or poweringdown the system. Upon insertion or removal of storage node 150 from slot142, the system automatically reconfigures in order to recognize andadapt to the change. Reconfiguration, in some embodiments, includesrestoring redundancy and/or rebalancing data or load.

Each storage node 150 can have multiple components. In the embodimentshown here, the storage node 150 includes a printed circuit board 159populated by a CPU 156, i.e., processor, a memory 154 coupled to the CPU156, and a non-volatile solid state storage 152 coupled to the CPU 156,although other mountings and/or components could be used in furtherembodiments. The memory 154 has instructions which are executed by theCPU 156 and/or data operated on by the CPU 156. As further explainedbelow, the non-volatile solid state storage 152 includes flash or, infurther embodiments, other types of solid-state memory.

Referring to FIG. 2A, storage cluster 161 is scalable, meaning thatstorage capacity with non-uniform storage sizes is readily added, asdescribed above. One or more storage nodes 150 can be plugged into orremoved from each chassis and the storage cluster self-configures insome embodiments. Plug-in storage nodes 150, whether installed in achassis as delivered or later added, can have different sizes. Forexample, in one embodiment a storage node 150 can have any multiple of 4TB, e.g., 8 TB, 12 TB, 16 TB, 32 TB, etc. In further embodiments, astorage node 150 could have any multiple of other storage amounts orcapacities. Storage capacity of each storage node 150 is broadcast, andinfluences decisions of how to stripe the data. For maximum storageefficiency, an embodiment can self-configure as wide as possible in thestripe, subject to a predetermined requirement of continued operationwith loss of up to one, or up to two, non-volatile solid state storageunits 152 or storage nodes 150 within the chassis.

FIG. 2B is a block diagram showing a communications interconnect 171A-Fand power distribution bus 172 coupling multiple storage nodes 150.Referring back to FIG. 2A, the communications interconnect 171A-F can beincluded in or implemented with the switch fabric 146 in someembodiments. Where multiple storage clusters 161 occupy a rack, thecommunications interconnect 171A-F can be included in or implementedwith a top of rack switch, in some embodiments. As illustrated in FIG.2B, storage cluster 161 is enclosed within a single chassis 138.External port 176 is coupled to storage nodes 150 through communicationsinterconnect 171A-F, while external port 174 is coupled directly to astorage node. External power port 178 is coupled to power distributionbus 172. Storage nodes 150 may include varying amounts and differingcapacities of non-volatile solid state storage 152 as described withreference to FIG. 2A. In addition, one or more storage nodes 150 may bea compute only storage node as illustrated in FIG. 2B. Authorities 168are implemented on the non-volatile solid state storages 152, forexample as lists or other data structures stored in memory. In someembodiments the authorities are stored within the non-volatile solidstate storage 152 and supported by software executing on a controller orother processor of the non-volatile solid state storage 152. In afurther embodiment, authorities 168 are implemented on the storage nodes150, for example as lists or other data structures stored in the memory154 and supported by software executing on the CPU 156 of the storagenode 150. Authorities 168 control how and where data is stored in thenon-volatile solid state storages 152 in some embodiments. This controlassists in determining which type of erasure coding scheme is applied tothe data, and which storage nodes 150 have which portions of the data.Each authority 168 may be assigned to a non-volatile solid state storage152. Each authority may control a range of inode numbers, segmentnumbers, or other data identifiers which are assigned to data by a filesystem, by the storage nodes 150, or by the non-volatile solid statestorage 152, in various embodiments.

Every piece of data, and every piece of metadata, has redundancy in thesystem in some embodiments. In addition, every piece of data and everypiece of metadata has an owner, which may be referred to as anauthority. If that authority is unreachable, for example through failureof a storage node, there is a plan of succession for how to find thatdata or that metadata. In various embodiments, there are redundantcopies of authorities 168. Authorities 168 have a relationship tostorage nodes 150 and non-volatile solid state storage 152 in someembodiments. Each authority 168, covering a range of data segmentnumbers or other identifiers of the data, may be assigned to a specificnon-volatile solid state storage 152. In some embodiments theauthorities 168 for all of such ranges are distributed over thenon-volatile solid state storages 152 of a storage cluster. Each storagenode 150 has a network port that provides access to the non-volatilesolid state storage(s) 152 of that storage node 150. Data can be storedin a segment, which is associated with a segment number and that segmentnumber is an indirection for a configuration of a RAID (redundant arrayof independent disks) stripe in some embodiments. The assignment and useof the authorities 168 thus establishes an indirection to data.Indirection may be referred to as the ability to reference dataindirectly, in this case via an authority 168, in accordance with someembodiments. A segment identifies a set of non-volatile solid statestorage 152 and a local identifier into the set of non-volatile solidstate storage 152 that may contain data. In some embodiments, the localidentifier is an offset into the device and may be reused sequentiallyby multiple segments. In other embodiments the local identifier isunique for a specific segment and never reused. The offsets in thenon-volatile solid state storage 152 are applied to locating data forwriting to or reading from the non-volatile solid state storage 152 (inthe form of a RAID stripe). Data is striped across multiple units ofnon-volatile solid state storage 152, which may include or be differentfrom the non-volatile solid state storage 152 having the authority 168for a particular data segment.

If there is a change in where a particular segment of data is located,e.g., during a data move or a data reconstruction, the authority 168 forthat data segment should be consulted, at that non-volatile solid statestorage 152 or storage node 150 having that authority 168. In order tolocate a particular piece of data, embodiments calculate a hash valuefor a data segment or apply an inode number or a data segment number.The output of this operation points to a non-volatile solid statestorage 152 having the authority 168 for that particular piece of data.In some embodiments there are two stages to this operation. The firststage maps an entity identifier (ID), e.g., a segment number, inodenumber, or directory number to an authority identifier. This mapping mayinclude a calculation such as a hash or a bit mask. The second stage ismapping the authority identifier to a particular non-volatile solidstate storage 152, which may be done through an explicit mapping. Theoperation is repeatable, so that when the calculation is performed, theresult of the calculation repeatably and reliably points to a particularnon-volatile solid state storage 152 having that authority 168. Theoperation may include the set of reachable storage nodes as input. Ifthe set of reachable non-volatile solid state storage units changes theoptimal set changes. In some embodiments, the persisted value is thecurrent assignment (which is always true) and the calculated value isthe target assignment the cluster will attempt to reconfigure towards.This calculation may be used to determine the optimal non-volatile solidstate storage 152 for an authority in the presence of a set ofnon-volatile solid state storage 152 that are reachable and constitutethe same cluster. The calculation also determines an ordered set of peernon-volatile solid state storage 152 that will also record the authorityto non-volatile solid state storage mapping so that the authority may bedetermined even if the assigned non-volatile solid state storage isunreachable. A duplicate or substitute authority 168 may be consulted ifa specific authority 168 is unavailable in some embodiments.

With reference to FIGS. 2A and 2B, two of the many tasks of the CPU 156on a storage node 150 are to break up write data, and reassemble readdata. When the system has determined that data is to be written, theauthority 168 for that data is located as above. When the segment ID fordata is already determined the request to write is forwarded to thenon-volatile solid state storage 152 currently determined to be the hostof the authority 168 determined from the segment. The host CPU 156 ofthe storage node 150, on which the non-volatile solid state storage 152and corresponding authority 168 reside, then breaks up or shards thedata and transmits the data out to various non-volatile solid statestorage 152. The transmitted data is written as a data stripe inaccordance with an erasure coding scheme. In some embodiments, data isrequested to be pulled, and in other embodiments, data is pushed. Inreverse, when data is read, the authority 168 for the segment IDcontaining the data is located as described above. The host CPU 156 ofthe storage node 150 on which the non-volatile solid state storage 152and corresponding authority 168 reside requests the data from thenon-volatile solid state storage and corresponding storage nodes pointedto by the authority. In some embodiments the data is read from flashstorage as a data stripe. The host CPU 156 of storage node 150 thenreassembles the read data, correcting any errors (if present) accordingto the appropriate erasure coding scheme, and forwards the reassembleddata to the network. In further embodiments, some or all of these taskscan be handled in the non-volatile solid state storage 152. In someembodiments, the segment host requests the data be sent to storage node150 by requesting pages from storage and then sending the data to thestorage node making the original request.

In some systems, for example in UNIX-style file systems, data is handledwith an index node or inode, which specifies a data structure thatrepresents an object in a file system. The object could be a file or adirectory, for example. Metadata may accompany the object, as attributessuch as permission data and a creation timestamp, among otherattributes. A segment number could be assigned to all or a portion ofsuch an object in a file system. In other systems, data segments arehandled with a segment number assigned elsewhere. For purposes ofdiscussion, the unit of distribution is an entity, and an entity can bea file, a directory or a segment. That is, entities are units of data ormetadata stored by a storage system. Entities are grouped into setscalled authorities. Each authority has an authority owner, which is astorage node that has the exclusive right to update the entities in theauthority. In other words, a storage node contains the authority, andthat the authority, in turn, contains entities.

A segment is a logical container of data in accordance with someembodiments. A segment is an address space between medium address spaceand physical flash locations, i.e., the data segment number, are in thisaddress space. Segments may also contain meta-data, which enable dataredundancy to be restored (rewritten to different flash locations ordevices) without the involvement of higher level software. In oneembodiment, an internal format of a segment contains client data andmedium mappings to determine the position of that data. Each datasegment is protected, e.g., from memory and other failures, by breakingthe segment into a number of data and parity shards, where applicable.The data and parity shards are distributed, i.e., striped, acrossnon-volatile solid state storage 152 coupled to the host CPUs 156 (SeeFIGS. 2E and 2G) in accordance with an erasure coding scheme. Usage ofthe term segments refers to the container and its place in the addressspace of segments in some embodiments. Usage of the term stripe refersto the same set of shards as a segment and includes how the shards aredistributed along with redundancy or parity information in accordancewith some embodiments.

A series of address-space transformations takes place across an entirestorage system. At the top are the directory entries (file names) whichlink to an inode. Inodes point into medium address space, where data islogically stored. Medium addresses may be mapped through a series ofindirect mediums to spread the load of large files, or implement dataservices like deduplication or snapshots. Medium addresses may be mappedthrough a series of indirect mediums to spread the load of large files,or implement data services like deduplication or snapshots. Segmentaddresses are then translated into physical flash locations. Physicalflash locations have an address range bounded by the amount of flash inthe system in accordance with some embodiments. Medium addresses andsegment addresses are logical containers, and in some embodiments use a128 bit or larger identifier so as to be practically infinite, with alikelihood of reuse calculated as longer than the expected life of thesystem. Addresses from logical containers are allocated in ahierarchical fashion in some embodiments. Initially, each non-volatilesolid state storage unit 152 may be assigned a range of address space.Within this assigned range, the non-volatile solid state storage 152 isable to allocate addresses without synchronization with othernon-volatile solid state storage 152.

Data and metadata is stored by a set of underlying storage layouts thatare optimized for varying workload patterns and storage devices. Theselayouts incorporate multiple redundancy schemes, compression formats andindex algorithms. Some of these layouts store information aboutauthorities and authority masters, while others store file metadata andfile data. The redundancy schemes include error correction codes thattolerate corrupted bits within a single storage device (such as a NANDflash chip), erasure codes that tolerate the failure of multiple storagenodes, and replication schemes that tolerate data center or regionalfailures. In some embodiments, low density parity check (‘LDPC’) code isused within a single storage unit. Reed-Solomon encoding is used withina storage cluster, and mirroring is used within a storage grid in someembodiments. Metadata may be stored using an ordered log structuredindex (such as a Log Structured Merge Tree), and large data may not bestored in a log structured layout.

In order to maintain consistency across multiple copies of an entity,the storage nodes agree implicitly on two things through calculations:(1) the authority that contains the entity, and (2) the storage nodethat contains the authority. The assignment of entities to authoritiescan be done by pseudo randomly assigning entities to authorities, bysplitting entities into ranges based upon an externally produced key, orby placing a single entity into each authority. Examples of pseudorandomschemes are linear hashing and the Replication Under Scalable Hashing(‘RUSH’) family of hashes, including Controlled Replication UnderScalable Hashing (‘CRUSH’). In some embodiments, pseudo-randomassignment is utilized only for assigning authorities to nodes becausethe set of nodes can change. The set of authorities cannot change so anysubjective function may be applied in these embodiments. Some placementschemes automatically place authorities on storage nodes, while otherplacement schemes rely on an explicit mapping of authorities to storagenodes. In some embodiments, a pseudorandom scheme is utilized to mapfrom each authority to a set of candidate authority owners. Apseudorandom data distribution function related to CRUSH may assignauthorities to storage nodes and create a list of where the authoritiesare assigned. Each storage node has a copy of the pseudorandom datadistribution function, and can arrive at the same calculation fordistributing, and later finding or locating an authority. Each of thepseudorandom schemes requires the reachable set of storage nodes asinput in some embodiments in order to conclude the same target nodes.Once an entity has been placed in an authority, the entity may be storedon physical devices so that no expected failure will lead to unexpecteddata loss. In some embodiments, rebalancing algorithms attempt to storethe copies of all entities within an authority in the same layout and onthe same set of machines.

Examples of expected failures include device failures, stolen machines,datacenter fires, and regional disasters, such as nuclear or geologicalevents. Different failures lead to different levels of acceptable dataloss. In some embodiments, a stolen storage node impacts neither thesecurity nor the reliability of the system, while depending on systemconfiguration, a regional event could lead to no loss of data, a fewseconds or minutes of lost updates, or even complete data loss.

In the embodiments, the placement of data for storage redundancy isindependent of the placement of authorities for data consistency. Insome embodiments, storage nodes that contain authorities do not containany persistent storage. Instead, the storage nodes are connected tonon-volatile solid state storage units that do not contain authorities.The communications interconnect between storage nodes and non-volatilesolid state storage units consists of multiple communicationtechnologies and has non-uniform performance and fault tolerancecharacteristics. In some embodiments, as mentioned above, non-volatilesolid state storage units are connected to storage nodes via PCIexpress, storage nodes are connected together within a single chassisusing Ethernet backplane, and chassis are connected together to form astorage cluster. Storage clusters are connected to clients usingEthernet or fiber channel in some embodiments. If multiple storageclusters are configured into a storage grid, the multiple storageclusters are connected using the Internet or other long-distancenetworking links, such as a “metro scale” link or private link that doesnot traverse the internet.

Authority owners have the exclusive right to modify entities, to migrateentities from one non-volatile solid state storage unit to anothernon-volatile solid state storage unit, and to add and remove copies ofentities. This allows for maintaining the redundancy of the underlyingdata. When an authority owner fails, is going to be decommissioned, oris overloaded, the authority is transferred to a new storage node.Transient failures make it non-trivial to ensure that all non-faultymachines agree upon the new authority location. The ambiguity thatarises due to transient failures can be achieved automatically by aconsensus protocol such as Paxos, hot-warm failover schemes, via manualintervention by a remote system administrator, or by a local hardwareadministrator (such as by physically removing the failed machine fromthe cluster, or pressing a button on the failed machine). In someembodiments, a consensus protocol is used, and failover is automatic. Iftoo many failures or replication events occur in too short a timeperiod, the system goes into a self-preservation mode and haltsreplication and data movement activities until an administratorintervenes in accordance with some embodiments.

As authorities are transferred between storage nodes and authorityowners update entities in their authorities, the system transfersmessages between the storage nodes and non-volatile solid state storageunits. With regard to persistent messages, messages that have differentpurposes are of different types. Depending on the type of the message,the system maintains different ordering and durability guarantees. Asthe persistent messages are being processed, the messages aretemporarily stored in multiple durable and non-durable storage hardwaretechnologies. In some embodiments, messages are stored in RAM, NVRAM andon NAND flash devices, and a variety of protocols are used in order tomake efficient use of each storage medium. Latency-sensitive clientrequests may be persisted in replicated NVRAM, and then later NAND,while background rebalancing operations are persisted directly to NAND.

Persistent messages are persistently stored prior to being transmitted.This allows the system to continue to serve client requests despitefailures and component replacement. Although many hardware componentscontain unique identifiers that are visible to system administrators,manufacturer, hardware supply chain and ongoing monitoring qualitycontrol infrastructure, applications running on top of theinfrastructure address virtualize addresses. These virtualized addressesdo not change over the lifetime of the storage system, regardless ofcomponent failures and replacements. This allows each component of thestorage system to be replaced over time without reconfiguration ordisruptions of client request processing, i.e., the system supportsnon-disruptive upgrades.

In some embodiments, the virtualized addresses are stored withsufficient redundancy. A continuous monitoring system correlateshardware and software status and the hardware identifiers. This allowsdetection and prediction of failures due to faulty components andmanufacturing details. The monitoring system also enables the proactivetransfer of authorities and entities away from impacted devices beforefailure occurs by removing the component from the critical path in someembodiments.

FIG. 2C is a multiple level block diagram, showing contents of a storagenode 150 and contents of a non-volatile solid state storage 152 of thestorage node 150. Data is communicated to and from the storage node 150by a network interface controller (‘NIC’) 202 in some embodiments. Eachstorage node 150 has a CPU 156, and one or more non-volatile solid statestorage 152, as discussed above. Moving down one level in FIG. 2C, eachnon-volatile solid state storage 152 has a relatively fast non-volatilesolid state memory, such as nonvolatile random access memory (‘NVRAM’)204, and flash memory 206. In some embodiments, NVRAM 204 may be acomponent that does not require program/erase cycles (DRAM, MRAM, PCM),and can be a memory that can support being written vastly more oftenthan the memory is read from. Moving down another level in FIG. 2C, theNVRAM 204 is implemented in one embodiment as high speed volatilememory, such as dynamic random access memory (DRAM) 216, backed up byenergy reserve 218. Energy reserve 218 provides sufficient electricalpower to keep the DRAM 216 powered long enough for contents to betransferred to the flash memory 206 in the event of power failure. Insome embodiments, energy reserve 218 is a capacitor, super-capacitor,battery, or other device, that supplies a suitable supply of energysufficient to enable the transfer of the contents of DRAM 216 to astable storage medium in the case of power loss. The flash memory 206 isimplemented as multiple flash dies 222, which may be referred to aspackages of flash dies 222 or an array of flash dies 222. It should beappreciated that the flash dies 222 could be packaged in any number ofways, with a single die per package, multiple dies per package (i.e.multichip packages), in hybrid packages, as bare dies on a printedcircuit board or other substrate, as encapsulated dies, etc. In theembodiment shown, the non-volatile solid state storage 152 has acontroller 212 or other processor, and an input output (I/O) port 210coupled to the controller 212. I/O port 210 is coupled to the CPU 156and/or the network interface controller 202 of the flash storage node150. Flash input output (I/O) port 220 is coupled to the flash dies 222,and a direct memory access unit (DMA) 214 is coupled to the controller212, the DRAM 216 and the flash dies 222. In the embodiment shown, theI/O port 210, controller 212, DMA unit 214 and flash I/O port 220 areimplemented on a programmable logic device (‘PLD’) 208, e.g., a fieldprogrammable gate array (FPGA). In this embodiment, each flash die 222has pages, organized as sixteen kB (kilobyte) pages 224, and a register226 through which data can be written to or read from the flash die 222.In further embodiments, other types of solid-state memory are used inplace of, or in addition to flash memory illustrated within flash die222.

Storage clusters 161, in various embodiments as disclosed herein, can becontrasted with storage arrays in general. The storage nodes 150 arepart of a collection that creates the storage cluster 161. Each storagenode 150 owns a slice of data and computing required to provide thedata. Multiple storage nodes 150 cooperate to store and retrieve thedata. Storage memory or storage devices, as used in storage arrays ingeneral, are less involved with processing and manipulating the data.Storage memory or storage devices in a storage array receive commands toread, write, or erase data. The storage memory or storage devices in astorage array are not aware of a larger system in which they areembedded, or what the data means. Storage memory or storage devices instorage arrays can include various types of storage memory, such as RAM,solid state drives, hard disk drives, etc. The storage units 152described herein have multiple interfaces active simultaneously andserving multiple purposes. In some embodiments, some of thefunctionality of a storage node 150 is shifted into a storage unit 152,transforming the storage unit 152 into a combination of storage unit 152and storage node 150. Placing computing (relative to storage data) intothe storage unit 152 places this computing closer to the data itself.The various system embodiments have a hierarchy of storage node layerswith different capabilities. By contrast, in a storage array, acontroller owns and knows everything about all of the data that thecontroller manages in a shelf or storage devices. In a storage cluster161, as described herein, multiple controllers in multiple storage units152 and/or storage nodes 150 cooperate in various ways (e.g., forerasure coding, data sharding, metadata communication and redundancy,storage capacity expansion or contraction, data recovery, and so on).

FIG. 2D shows a storage server environment, which uses embodiments ofthe storage nodes 150 and storage units 152 of FIGS. 2A-C. In thisversion, each storage unit 152 has a processor such as controller 212(see FIG. 2C), an FPGA (field programmable gate array), flash memory206, and NVRAM 204 (which is super-capacitor backed DRAM 216, see FIGS.2B and 2C) on a PCIe (peripheral component interconnect express) boardin a chassis 138 (see FIG. 2A). The storage unit 152 may be implementedas a single board containing storage, and may be the largest tolerablefailure domain inside the chassis. In some embodiments, up to twostorage units 152 may fail and the device will continue with no dataloss.

The physical storage is divided into named regions based on applicationusage in some embodiments. The NVRAM 204 is a contiguous block ofreserved memory in the storage unit 152 DRAM 216, and is backed by NANDflash. NVRAM 204 is logically divided into multiple memory regionswritten for two as spool (e.g., spool_region). Space within the NVRAM204 spools is managed by each authority 168 independently. Each deviceprovides an amount of storage space to each authority 168. Thatauthority 168 further manages lifetimes and allocations within thatspace. Examples of a spool include distributed transactions or notions.When the primary power to a storage unit 152 fails, onboardsuper-capacitors provide a short duration of power hold up. During thisholdup interval, the contents of the NVRAM 204 are flushed to flashmemory 206. On the next power-on, the contents of the NVRAM 204 arerecovered from the flash memory 206.

As for the storage unit controller, the responsibility of the logical“controller” is distributed across each of the blades containingauthorities 168. This distribution of logical control is shown in FIG.2D as a host controller 242, mid-tier controller 244 and storage unitcontroller(s) 246. Management of the control plane and the storage planeare treated independently, although parts may be physically co-locatedon the same blade. Each authority 168 effectively serves as anindependent controller. Each authority 168 provides its own data andmetadata structures, its own background workers, and maintains its ownlifecycle.

FIG. 2E is a blade 252 hardware block diagram, showing a control plane254, compute and storage planes 256, 258, and authorities 168interacting with underlying physical resources, using embodiments of thestorage nodes 150 and storage units 152 of FIGS. 2A-C in the storageserver environment of FIG. 2D. The control plane 254 is partitioned intoa number of authorities 168 which can use the compute resources in thecompute plane 256 to run on any of the blades 252. The storage plane 258is partitioned into a set of devices, each of which provides access toflash 206 and NVRAM 204 resources.

In the compute and storage planes 256, 258 of FIG. 2E, the authorities168 interact with the underlying physical resources (i.e., devices).From the point of view of an authority 168, its resources are stripedover all of the physical devices. From the point of view of a device, itprovides resources to all authorities 168, irrespective of where theauthorities happen to run. Each authority 168 has allocated or has beenallocated one or more partitions 260 of storage memory in the storageunits 152, e.g. partitions 260 in flash memory 206 and NVRAM 204. Eachauthority 168 uses those allocated partitions 260 that belong to it, forwriting or reading user data. Authorities can be associated withdiffering amounts of physical storage of the system. For example, oneauthority 168 could have a larger number of partitions 260 or largersized partitions 260 in one or more storage units 152 than one or moreother authorities 168.

FIG. 2F depicts elasticity software layers in blades 252 of a storagecluster, in accordance with some embodiments. In the elasticitystructure, elasticity software is symmetric, i.e., each blade's computemodule 270 runs the three identical layers of processes depicted in FIG.2F. Storage managers 274 execute read and write requests from otherblades 252 for data and metadata stored in local storage unit 152 NVRAM204 and flash 206. Authorities 168 fulfill client requests by issuingthe necessary reads and writes to the blades 252 on whose storage units152 the corresponding data or metadata resides. Endpoints 272 parseclient connection requests received from switch fabric 146 supervisorysoftware, relay the client connection requests to the authorities 168responsible for fulfillment, and relay the authorities' 168 responses toclients. The symmetric three-layer structure enables the storagesystem's high degree of concurrency. Elasticity scales out efficientlyand reliably in these embodiments. In addition, elasticity implements aunique scale-out technique that balances work evenly across allresources regardless of client access pattern, and maximizes concurrencyby eliminating much of the need for inter-blade coordination thattypically occurs with conventional distributed locking.

Still referring to FIG. 2F, authorities 168 running in the computemodules 270 of a blade 252 perform the internal operations required tofulfill client requests. One feature of elasticity is that authorities168 are stateless, i.e., they cache active data and metadata in theirown blades' 252 DRAMs for fast access, but the authorities store everyupdate in their NVRAM 204 partitions on three separate blades 252 untilthe update has been written to flash 206. All the storage system writesto NVRAM 204 are in triplicate to partitions on three separate blades252 in some embodiments. With triple-mirrored NVRAM 204 and persistentstorage protected by parity and Reed-Solomon RAID checksums, the storagesystem can survive concurrent failure of two blades 252 with no loss ofdata, metadata, or access to either.

Because authorities 168 are stateless, they can migrate between blades252. Each authority 168 has a unique identifier. NVRAM 204 and flash 206partitions are associated with authorities' 168 identifiers, not withthe blades 252 on which they are running in some. Thus, when anauthority 168 migrates, the authority 168 continues to manage the samestorage partitions from its new location. When a new blade 252 isinstalled in an embodiment of the storage cluster, the systemautomatically rebalances load by: partitioning the new blade's 252storage for use by the system's authorities 168, migrating selectedauthorities 168 to the new blade 252, starting endpoints 272 on the newblade 252 and including them in the switch fabric's 146 clientconnection distribution algorithm.

From their new locations, migrated authorities 168 persist the contentsof their NVRAM 204 partitions on flash 206, process read and writerequests from other authorities 168, and fulfill the client requeststhat endpoints 272 direct to them. Similarly, if a blade 252 fails or isremoved, the system redistributes its authorities 168 among the system'sremaining blades 252. The redistributed authorities 168 continue toperform their original functions from their new locations.

FIG. 2G depicts authorities 168 and storage resources in blades 252 of astorage cluster, in accordance with some embodiments. Each authority 168is exclusively responsible for a partition of the flash 206 and NVRAM204 on each blade 252. The authority 168 manages the content andintegrity of its partitions independently of other authorities 168.Authorities 168 compress incoming data and preserve it temporarily intheir NVRAM 204 partitions, and then consolidate, RAID-protect, andpersist the data in segments of the storage in their flash 206partitions. As the authorities 168 write data to flash 206, storagemanagers 274 perform the necessary flash translation to optimize writeperformance and maximize media longevity. In the background, authorities168 “garbage collect,” or reclaim space occupied by data that clientshave made obsolete by overwriting the data. It should be appreciatedthat since authorities' 168 partitions are disjoint, there is no needfor distributed locking to execute client and writes or to performbackground functions.

The embodiments described herein may utilize various software,communication and/or networking protocols. In addition, theconfiguration of the hardware and/or software may be adjusted toaccommodate various protocols. For example, the embodiments may utilizeActive Directory, which is a database based system that providesauthentication, directory, policy, and other services in a WINDOWS™environment. In these embodiments, LDAP (Lightweight Directory AccessProtocol) is one example application protocol for querying and modifyingitems in directory service providers such as Active Directory. In someembodiments, a network lock manager (‘NLM’) is utilized as a facilitythat works in cooperation with the Network File System (‘NFS’) toprovide a System V style of advisory file and record locking over anetwork. The Server Message Block (‘SMB’) protocol, one version of whichis also known as Common Internet File System (‘CIFS’), may be integratedwith the storage systems discussed herein. SMP operates as anapplication-layer network protocol typically used for providing sharedaccess to files, printers, and serial ports and miscellaneouscommunications between nodes on a network. SMB also provides anauthenticated inter-process communication mechanism. AMAZON™ S3 (SimpleStorage Service) is a web service offered by Amazon Web Services, andthe systems described herein may interface with Amazon S3 through webservices interfaces (REST (representational state transfer), SOAP(simple object access protocol), and BitTorrent). A RESTful API(application programming interface) breaks down a transaction to createa series of small modules. Each module addresses a particular underlyingpart of the transaction. The control or permissions provided with theseembodiments, especially for object data, may include utilization of anaccess control list (‘ACL’). The ACL is a list of permissions attachedto an object and the ACL specifies which users or system processes aregranted access to objects, as well as what operations are allowed ongiven objects. The systems may utilize Internet Protocol version 6(‘IPv6’), as well as IPv4, for the communications protocol that providesan identification and location system for computers on networks androutes traffic across the Internet. The routing of packets betweennetworked systems may include Equal-cost multi-path routing (‘ECMP’),which is a routing strategy where next-hop packet forwarding to a singledestination can occur over multiple “best paths” which tie for top placein routing metric calculations. Multi-path routing can be used inconjunction with most routing protocols, because it is a per-hopdecision limited to a single router. The software may supportMulti-tenancy, which is an architecture in which a single instance of asoftware application serves multiple customers. Each customer may bereferred to as a tenant. Tenants may be given the ability to customizesome parts of the application, but may not customize the application'scode, in some embodiments. The embodiments may maintain audit logs. Anaudit log is a document that records an event in a computing system. Inaddition to documenting what resources were accessed, audit log entriestypically include destination and source addresses, a timestamp, anduser login information for compliance with various regulations. Theembodiments may support various key management policies, such asencryption key rotation. In addition, the system may support dynamicroot passwords or some variation dynamically changing passwords.

FIG. 3A sets forth a diagram of a storage system 306 that is coupled fordata communications with a cloud services provider 302 in accordancewith some embodiments of the present disclosure. Although depicted inless detail, the storage system 306 depicted in FIG. 3A may be similarto the storage systems described above with reference to FIGS. 1A-1D andFIGS. 2A-2G. In some embodiments, the storage system 306 depicted inFIG. 3A may be embodied as a storage system that includes imbalancedactive/active controllers, as a storage system that includes balancedactive/active controllers, as a storage system that includesactive/active controllers where less than all of each controller'sresources are utilized such that each controller has reserve resourcesthat may be used to support failover, as a storage system that includesfully active/active controllers, as a storage system that includesdataset-segregated controllers, as a storage system that includesdual-layer architectures with front-end controllers and back-endintegrated storage controllers, as a storage system that includesscale-out clusters of dual-controller arrays, as well as combinations ofsuch embodiments.

In the example depicted in FIG. 3A, the storage system 306 is coupled tothe cloud services provider 302 via a data communications link 304. Thedata communications link 304 may be embodied as a dedicated datacommunications link, as a data communications pathway that is providedthrough the use of one or data communications networks such as a widearea network (‘WAN’) or local area network (‘LAN’), or as some othermechanism capable of transporting digital information between thestorage system 306 and the cloud services provider 302. Such a datacommunications link 304 may be fully wired, fully wireless, or someaggregation of wired and wireless data communications pathways. In suchan example, digital information may be exchanged between the storagesystem 306 and the cloud services provider 302 via the datacommunications link 304 using one or more data communications protocols.For example, digital information may be exchanged between the storagesystem 306 and the cloud services provider 302 via the datacommunications link 304 using the handheld device transfer protocol(‘HDTP’), hypertext transfer protocol (‘HTTP’), internet protocol(‘IP’), real-time transfer protocol (‘RTP’), transmission controlprotocol (‘TCP’), user datagram protocol (‘UDP’), wireless applicationprotocol (‘WAP’), or other protocol.

The cloud services provider 302 depicted in FIG. 3A may be embodied, forexample, as a system and computing environment that provides services tousers of the cloud services provider 302 through the sharing ofcomputing resources via the data communications link 304. The cloudservices provider 302 may provide on-demand access to a shared pool ofconfigurable computing resources such as computer networks, servers,storage, applications and services, and so on. The shared pool ofconfigurable resources may be rapidly provisioned and released to a userof the cloud services provider 302 with minimal management effort.Generally, the user of the cloud services provider 302 is unaware of theexact computing resources utilized by the cloud services provider 302 toprovide the services. Although in many cases such a cloud servicesprovider 302 may be accessible via the Internet, readers of skill in theart will recognize that any system that abstracts the use of sharedresources to provide services to a user through any data communicationslink may be considered a cloud services provider 302.

In the example depicted in FIG. 3A, the cloud services provider 302 maybe configured to provide a variety of services to the storage system 306and users of the storage system 306 through the implementation ofvarious service models. For example, the cloud services provider 302 maybe configured to provide services to the storage system 306 and users ofthe storage system 306 through the implementation of an infrastructureas a service (‘IaaS’) service model where the cloud services provider302 offers computing infrastructure such as virtual machines and otherresources as a service to subscribers. In addition, the cloud servicesprovider 302 may be configured to provide services to the storage system306 and users of the storage system 306 through the implementation of aplatform as a service (‘PaaS’) service model where the cloud servicesprovider 302 offers a development environment to application developers.Such a development environment may include, for example, an operatingsystem, programming-language execution environment, database, webserver, or other components that may be utilized by applicationdevelopers to develop and run software solutions on a cloud platform.Furthermore, the cloud services provider 302 may be configured toprovide services to the storage system 306 and users of the storagesystem 306 through the implementation of a software as a service(‘SaaS’) service model where the cloud services provider 302 offersapplication software, databases, as well as the platforms that are usedto run the applications to the storage system 306 and users of thestorage system 306, providing the storage system 306 and users of thestorage system 306 with on-demand software and eliminating the need toinstall and run the application on local computers, which may simplifymaintenance and support of the application. The cloud services provider302 may be further configured to provide services to the storage system306 and users of the storage system 306 through the implementation of anauthentication as a service (‘AaaS’) service model where the cloudservices provider 302 offers authentication services that can be used tosecure access to applications, data sources, or other resources. Thecloud services provider 302 may also be configured to provide servicesto the storage system 306 and users of the storage system 306 throughthe implementation of a storage as a service model where the cloudservices provider 302 offers access to its storage infrastructure foruse by the storage system 306 and users of the storage system 306.Readers will appreciate that the cloud services provider 302 may beconfigured to provide additional services to the storage system 306 andusers of the storage system 306 through the implementation of additionalservice models, as the service models described above are included onlyfor explanatory purposes and in no way represent a limitation of theservices that may be offered by the cloud services provider 302 or alimitation as to the service models that may be implemented by the cloudservices provider 302.

In the example depicted in FIG. 3A, the cloud services provider 302 maybe embodied, for example, as a private cloud, as a public cloud, or as acombination of a private cloud and public cloud. In an embodiment inwhich the cloud services provider 302 is embodied as a private cloud,the cloud services provider 302 may be dedicated to providing servicesto a single organization rather than providing services to multipleorganizations. In an embodiment where the cloud services provider 302 isembodied as a public cloud, the cloud services provider 302 may provideservices to multiple organizations. Public cloud and private clouddeployment models may differ and may come with various advantages anddisadvantages. For example, because a public cloud deployment involvesthe sharing of a computing infrastructure across different organization,such a deployment may not be ideal for organizations with securityconcerns, mission-critical workloads, uptime requirements demands, andso on. While a private cloud deployment can address some of theseissues, a private cloud deployment may require on-premises staff tomanage the private cloud. In still alternative embodiments, the cloudservices provider 302 may be embodied as a mix of a private and publiccloud services with a hybrid cloud deployment.

Although not explicitly depicted in FIG. 3A, readers will appreciatethat additional hardware components and additional software componentsmay be necessary to facilitate the delivery of cloud services to thestorage system 306 and users of the storage system 306. For example, thestorage system 306 may be coupled to (or even include) a cloud storagegateway. Such a cloud storage gateway may be embodied, for example, ashardware-based or software-based appliance that is located on premisewith the storage system 306. Such a cloud storage gateway may operate asa bridge between local applications that are executing on the storagearray 306 and remote, cloud-based storage that is utilized by thestorage array 306. Through the use of a cloud storage gateway,organizations may move primary iSCSI or NAS to the cloud servicesprovider 302, thereby enabling the organization to save space on theiron-premises storage systems. Such a cloud storage gateway may beconfigured to emulate a disk array, a block-based device, a file server,or other storage system that can translate the SCSI commands, fileserver commands, or other appropriate command into REST-space protocolsthat facilitate communications with the cloud services provider 302.

In order to enable the storage system 306 and users of the storagesystem 306 to make use of the services provided by the cloud servicesprovider 302, a cloud migration process may take place during whichdata, applications, or other elements from an organization's localsystems (or even from another cloud environment) are moved to the cloudservices provider 302. In order to successfully migrate data,applications, or other elements to the cloud services provider's 302environment, middleware such as a cloud migration tool may be utilizedto bridge gaps between the cloud services provider's 302 environment andan organization's environment. Such cloud migration tools may also beconfigured to address potentially high network costs and long transfertimes associated with migrating large volumes of data to the cloudservices provider 302, as well as addressing security concernsassociated with sensitive data to the cloud services provider 302 overdata communications networks. In order to further enable the storagesystem 306 and users of the storage system 306 to make use of theservices provided by the cloud services provider 302, a cloudorchestrator may also be used to arrange and coordinate automated tasksin pursuit of creating a consolidated process or workflow. Such a cloudorchestrator may perform tasks such as configuring various components,whether those components are cloud components or on-premises components,as well as managing the interconnections between such components. Thecloud orchestrator can simplify the inter-component communication andconnections to ensure that links are correctly configured andmaintained.

In the example depicted in FIG. 3A, and as described briefly above, thecloud services provider 302 may be configured to provide services to thestorage system 306 and users of the storage system 306 through the usageof a SaaS service model where the cloud services provider 302 offersapplication software, databases, as well as the platforms that are usedto run the applications to the storage system 306 and users of thestorage system 306, providing the storage system 306 and users of thestorage system 306 with on-demand software and eliminating the need toinstall and run the application on local computers, which may simplifymaintenance and support of the application. Such applications may takemany forms in accordance with various embodiments of the presentdisclosure. For example, the cloud services provider 302 may beconfigured to provide access to data analytics applications to thestorage system 306 and users of the storage system 306. Such dataanalytics applications may be configured, for example, to receivetelemetry data phoned home by the storage system 306. Such telemetrydata may describe various operating characteristics of the storagesystem 306 and may be analyzed, for example, to determine the health ofthe storage system 306, to identify workloads that are executing on thestorage system 306, to predict when the storage system 306 will run outof various resources, to recommend configuration changes, hardware orsoftware upgrades, workflow migrations, or other actions that mayimprove the operation of the storage system 306.

The cloud services provider 302 may also be configured to provide accessto virtualized computing environments to the storage system 306 andusers of the storage system 306. Such virtualized computing environmentsmay be embodied, for example, as a virtual machine or other virtualizedcomputer hardware platforms, virtual storage devices, virtualizedcomputer network resources, and so on. Examples of such virtualizedenvironments can include virtual machines that are created to emulate anactual computer, virtualized desktop environments that separate alogical desktop from a physical machine, virtualized file systems thatallow uniform access to different types of concrete file systems, andmany others.

For further explanation, FIG. 3B sets forth a diagram of a storagesystem 306 in accordance with some embodiments of the presentdisclosure. Although depicted in less detail, the storage system 306depicted in FIG. 3B may be similar to the storage systems describedabove with reference to FIGS. 1A-1D and FIGS. 2A-2G as the storagesystem may include many of the components described above.

The storage system 306 depicted in FIG. 3B may include storage resources308, which may be embodied in many forms. For example, in someembodiments the storage resources 308 can include nano-RAM or anotherform of nonvolatile random access memory that utilizes carbon nanotubesdeposited on a substrate. In some embodiments, the storage resources 308may include 3D crosspoint non-volatile memory in which bit storage isbased on a change of bulk resistance, in conjunction with a stackablecross-gridded data access array. In some embodiments, the storageresources 308 may include flash memory, including single-level cell(‘SLC’) NAND flash, multi-level cell (‘MLC’) NAND flash, triple-levelcell (‘TLC’) NAND flash, quad-level cell (‘QLC’) NAND flash, and others.In some embodiments, the storage resources 308 may include non-volatilemagnetoresistive random-access memory (‘MRAM’), including spin transfertorque (‘STT’) MRAM, in which data is stored through the use of magneticstorage elements. In some embodiments, the example storage resources 308may include non-volatile phase-change memory (‘PCM’) that may have theability to hold multiple bits in a single cell as cells can achieve anumber of distinct intermediary states. In some embodiments, the storageresources 308 may include quantum memory that allows for the storage andretrieval of photonic quantum information. In some embodiments, theexample storage resources 308 may include resistive random-access memory(‘ReRAM’) in which data is stored by changing the resistance across adielectric solid-state material. In some embodiments, the storageresources 308 may include storage class memory (‘SCM’) in whichsolid-state nonvolatile memory may be manufactured at a high densityusing some combination of sub-lithographic patterning techniques,multiple bits per cell, multiple layers of devices, and so on. Readerswill appreciate that other forms of computer memories and storagedevices may be utilized by the storage systems described above,including DRAM, SRAM, EEPROM, universal memory, and many others. Thestorage resources 308 depicted in FIG. 3A may be embodied in a varietyof form factors, including but not limited to, dual in-line memorymodules (‘DIMMs’), non-volatile dual in-line memory modules (‘NVDIMMs’),M.2, U.2, and others.

The example storage system 306 depicted in FIG. 3B may implement avariety of storage architectures. For example, storage systems inaccordance with some embodiments of the present disclosure may utilizeblock storage where data is stored in blocks, and each block essentiallyacts as an individual hard drive. Storage systems in accordance withsome embodiments of the present disclosure may utilize object storage,where data is managed as objects. Each object may include the dataitself, a variable amount of metadata, and a globally unique identifier,where object storage can be implemented at multiple levels (e.g., devicelevel, system level, interface level). Storage systems in accordancewith some embodiments of the present disclosure utilize file storage inwhich data is stored in a hierarchical structure. Such data may be savedin files and folders, and presented to both the system storing it andthe system retrieving it in the same format.

The example storage system 306 depicted in FIG. 3B may be embodied as astorage system in which additional storage resources can be addedthrough the use of a scale-up model, additional storage resources can beadded through the use of a scale-out model, or through some combinationthereof. In a scale-up model, additional storage may be added by addingadditional storage devices. In a scale-out model, however, additionalstorage nodes may be added to a cluster of storage nodes, where suchstorage nodes can include additional processing resources, additionalnetworking resources, and so on.

The storage system 306 depicted in FIG. 3B also includes communicationsresources 310 that may be useful in facilitating data communicationsbetween components within the storage system 306, as well as datacommunications between the storage system 306 and computing devices thatare outside of the storage system 306. The communications resources 310may be configured to utilize a variety of different protocols and datacommunication fabrics to facilitate data communications betweencomponents within the storage systems as well as computing devices thatare outside of the storage system. For example, the communicationsresources 310 can include fibre channel (‘FC’) technologies such as FCfabrics and FC protocols that can transport SCSI commands over FCnetworks. The communications resources 310 can also include FC overethernet (‘FCoE’) technologies through which FC frames are encapsulatedand transmitted over Ethernet networks. The communications resources 310can also include InfiniBand (‘IB’) technologies in which a switchedfabric topology is utilized to facilitate transmissions between channeladapters. The communications resources 310 can also include NVM Express(‘NVMe’) technologies and NVMe over fabrics (‘NVMeoF’) technologiesthrough which non-volatile storage media attached via a PCI express(‘PCIe’) bus may be accessed. The communications resources 310 can alsoinclude mechanisms for accessing storage resources 308 within thestorage system 306 utilizing serial attached SCSI (‘SAS’), serial ATA(‘SATA’) bus interfaces for connecting storage resources 308 within thestorage system 306 to host bus adapters within the storage system 306,internet small computer systems interface (‘iSCSI’) technologies toprovide block-level access to storage resources 308 within the storagesystem 306, and other communications resources that that may be usefulin facilitating data communications between components within thestorage system 306, as well as data communications between the storagesystem 306 and computing devices that are outside of the storage system306.

The storage system 306 depicted in FIG. 3B also includes processingresources 312 that may be useful in useful in executing computer programinstructions and performing other computational tasks within the storagesystem 306. The processing resources 312 may include one or moreapplication-specific integrated circuits (‘ASICs’) that are customizedfor some particular purpose as well as one or more central processingunits (‘CPUs’). The processing resources 312 may also include one ormore digital signal processors (‘DSPs’), one or more field-programmablegate arrays (‘FPGAs’), one or more systems on a chip (‘SoCs’), or otherform of processing resources 312. The storage system 306 may utilize thestorage resources 312 to perform a variety of tasks including, but notlimited to, supporting the execution of software resources 314 that willbe described in greater detail below.

The storage system 306 depicted in FIG. 3B also includes softwareresources 314 that, when executed by processing resources 312 within thestorage system 306, may perform various tasks. The software resources314 may include, for example, one or more modules of computer programinstructions that when executed by processing resources 312 within thestorage system 306 are useful in carrying out various data protectiontechniques to preserve the integrity of data that is stored within thestorage systems. Readers will appreciate that such data protectiontechniques may be carried out, for example, by system software executingon computer hardware within the storage system, by a cloud servicesprovider, or in other ways. Such data protection techniques can include,for example, data archiving techniques that cause data that is no longeractively used to be moved to a separate storage device or separatestorage system for long-term retention, data backup techniques throughwhich data stored in the storage system may be copied and stored in adistinct location to avoid data loss in the event of equipment failureor some other form of catastrophe with the storage system, datareplication techniques through which data stored in the storage systemis replicated to another storage system such that the data may beaccessible via multiple storage systems, data snapshotting techniquesthrough which the state of data within the storage system is captured atvarious points in time, data and database cloning techniques throughwhich duplicate copies of data and databases may be created, and otherdata protection techniques. Through the use of such data protectiontechniques, business continuity and disaster recovery objectives may bemet as a failure of the storage system may not result in the loss ofdata stored in the storage system.

The software resources 314 may also include software that is useful inimplementing software-defined storage (‘SDS’). In such an example, thesoftware resources 314 may include one or more modules of computerprogram instructions that, when executed, are useful in policy-basedprovisioning and management of data storage that is independent of theunderlying hardware. Such software resources 314 may be useful inimplementing storage virtualization to separate the storage hardwarefrom the software that manages the storage hardware.

The software resources 314 may also include software that is useful infacilitating and optimizing I/O operations that are directed to thestorage resources 308 in the storage system 306. For example, thesoftware resources 314 may include software modules that perform carryout various data reduction techniques such as, for example, datacompression, data deduplication, and others. The software resources 314may include software modules that intelligently group together I/Ooperations to facilitate better usage of the underlying storage resource308, software modules that perform data migration operations to migratefrom within a storage system, as well as software modules that performother functions. Such software resources 314 may be embodied as one ormore software containers or in many other ways.

Readers will appreciate that the various components depicted in FIG. 3Bmay be grouped into one or more optimized computing packages asconverged infrastructures. Such converged infrastructures may includepools of computers, storage and networking resources that can be sharedby multiple applications and managed in a collective manner usingpolicy-driven processes. Such converged infrastructures may minimizecompatibility issues between various components within the storagesystem 306 while also reducing various costs associated with theestablishment and operation of the storage system 306. Such convergedinfrastructures may be implemented with a converged infrastructurereference architecture, with standalone appliances, with a softwaredriven hyper-converged approach, or in other ways.

Readers will appreciate that the storage system 306 depicted in FIG. 3Bmay be useful for supporting various types of software applications. Forexample, the storage system 306 may be useful in supporting artificialintelligence applications, database applications, DevOps projects,electronic design automation tools, event-driven software applications,high performance computing applications, simulation applications,high-speed data capture and analysis applications, machine learningapplications, media production applications, media serving applications,picture archiving and communication systems (‘PACS’) applications,software development applications, and many other types of applicationsby providing storage resources to such applications.

The storage systems described above may operate to support a widevariety of applications. In view of the fact that the storage systemsinclude compute resources, storage resources, and a wide variety ofother resources, the storage systems may be well suited to supportapplications that are resource intensive such as, for example,artificial intelligence applications. Such artificial intelligenceapplications may enable devices to perceive their environment and takeactions that maximize their chance of success at some goal. The storagesystems described above may also be well suited to support other typesof applications that are resource intensive such as, for example,machine learning applications. Machine learning applications may performvarious types of data analysis to automate analytical model building.Using algorithms that iteratively learn from data, machine learningapplications can enable computers to learn without being explicitlyprogrammed.

In addition to the resources already described, the storage systemsdescribed above may also include graphics processing units (‘GPUs’),occasionally referred to as visual processing unit (‘VPUs’). Such GPUsmay be embodied as specialized electronic circuits that rapidlymanipulate and alter memory to accelerate the creation of images in aframe buffer intended for output to a display device. Such GPUs may beincluded within any of the computing devices that are part of thestorage systems described above.

For further explanation, FIG. 4 sets forth a flow chart illustrating anexample method for ensuring the appropriate utilization of systemresources using weighted workload based, time-independent schedulingaccording to embodiments of the present disclosure. The example methoddepicted in FIG. 4 may be carried out, for example, by a storage systemthat is identical to or similar to the storage systems described abovewith reference to FIGS. 1-3 , as the storage system (404) can includestorage devices (422, 424, 426) as well as many of the other componentsdescribed in the previous figures.

The example method depicted in FIG. 4 includes receiving (406) an I/Orequest (402) associated with an entity. The I/O request (402) may bereceived (406), for example, via a SAN that connects users of thestorage system (404) to the storage system (404). In such an example,the I/O request (406) may be associated with a particular entity suchas, for example, a particular user of the storage system (404), aparticular user-visible entity such as a volume that is supported by thestorage system (404), a particular system-visible entity such as amedium that is supported by the storage system (404), or any otherentity that may be associated with an I/O request (402). The I/O request(402) that is received (406) may be embodied, for example, as a requestto write data to the storage system (404), as a request to read datafrom the storage system (404), or as another type of I/O request.

The example method depicted in FIG. 4 also includes determining (408)whether an amount of system resources required to service the I/Orequest (402) is greater than an amount of available system resources inthe storage system (404). The amount of system resources required toservice the I/O request (402) may be expressed, for example, in terms ofthe amount of processing resources required to service the I/O request(402), in terms of the amount of storage capacity required to servicethe I/O request (402), in terms of the amount of network bandwidthrequired to service the I/O request (402), or in other quantifiableterms. Readers will appreciate that the amount of system resourcesrequired to service the I/O request (402) may also be expressed in termssuch as a unit of I/O requests that is established by a systemadministrator, established by a scheduling module as described abovewith reference to FIG. 2 , or established by some other entity. A unitof I/O requests may be used in a debit/credit system that will bedescribed in greater detail below and may be representative of thecumulative amount of system resources of many types (e.g., processing,network, storage) that are generally consumed when servicing differenttypes of I/O requests. Consider an example in which the following tablerepresents the amount of system resources required to service differenttypes of I/O requests:

TABLE 1 Resource Consumption Table I/O Type Resources Required toService I/O Read (64 KB or less) 1 Read (over 64 KB) 2 Write (64 KB orless) 5 Write (over 64 KB) 10

In the resource consumption table included above, the amount ofresources required to service various types of I/O requests areexpressed units of I/O requests. The particular value associated witheach type of I/O request may be determined, for example, by determiningthe number of I/O requests of each type that may be executed in parallelby the storage system (404) while meeting a predetermined performancethreshold. For example, if all I/O requests should be serviced within aresponse time of 100 ms, through the use of testing operations it may bedetermined that the storage system (404) can execute ten times thenumber of read operations of 64 KB or less in parallel than the storagesystem (404) can execute write operations over 64 KB in size inparallel. As such, a write operation of over 64 KB in size required tentimes more system resources to be consumed relative to a read operationof 64 KB or less.

Readers will appreciate that in the example method depicted in FIG. 4 ,the storage system (404) may not be able to service an unlimited numberof I/O requests in parallel, especially while meeting the predeterminedperformance threshold. Through testing or observation of the actualoperation of the storage system (404) it may be determined, for example,that the storage system (404) can execute 1000 read operations of 64 KBor less in parallel while meeting the predetermined performancethreshold. Likewise, it may be determined that the storage system (404)can execute 100 write operations of over 64 KB in size in parallel whilemeeting the predetermined performance threshold. In such an example,using the resource consumption table included above, the storage system(404) would be able to execute 1000 units of I/O requests in parallelwhile meeting the predetermined performance threshold.

In the example method depicted in FIG. 4 , the amount of availablesystem resources in the storage system (404) may represent the portionof total system capacity that is not currently in use. Continuing withthe example described above in which the storage system (404) would beable to execute 1000 units of I/O requests in parallel while meeting thepredetermined performance threshold, assume that the storage system(404) is currently executing 100 read operations of 64 KB or less, 100read operations of over 64 KB in size, 100 write operations of 64 KB orless, and 15 write operations of over 64 KB in size. Using the resourceconsumption table included above, the 100 read operations of 64 KB orless would consume 100 units of I/O requests, the 100 read operations ofover 64 KB in size would consume 200 units of I/O requests, the 100write operations of 64 KB or less would consume 500 units of I/Orequests, and the 15 write operations of over 64 KB in size wouldconsume 150 units of I/O requests. As such, the amount of availablesystem resources in the storage system (404) would be 50 units of I/Orequests, as 950 units of I/O requests are currently being consumed bythe I/O requests currently executing on the storage system (404).

In the example method depicted in FIG. 4 , determining (408) whether anamount of system resources required to service the I/O request (402) isgreater than an amount of available system resources in the storagesystem (404) may be carried out, for example, by determining amount ofsystem resources required to service the I/O request (402) from aresource such as the resource consumption table included above andcomparing the amount of system resources required to service the I/Orequest (402) to the amount of available system resources in the storagesystem (404). In such an example, in response to determining that theamount of system resources required to service the I/O request is not(416) greater than the amount of available system resources in thestorage system, the I/O request (402) may be issued (420) to the storagesystem (404) for immediate processing by the storage system (404).Readers will appreciate that all I/O requests (402) that are receivedmay be issued (420) to the storage system (404) for immediate processingby the storage system (404) so long as the amount of system resourcesrequired to service the I/O request is not (416) greater than the amountof available system resources in the storage system and so long as thereare no other requests that are already queued and awaiting to bedispatched. In such an example, any requests that are already queued andwaiting to be dispatched may be issued first to maintain I/O ordering(as much as possible) and to avoid queueing requests indefinitely.

The example method depicted in FIG. 4 also includes, responsive toaffirmatively (410) determining that the amount of system resourcesrequired to service the I/O request (402) is greater than the amount ofavailable system resources in the storage system (404), queueing (412)the I/O request (402) in an entity-specific queue for the entity that isassociated with the I/O request (402). Readers will appreciate thatissuing the I/O request (402) to the storage system (404) when theamount of system resources required to service the I/O request (402) isgreater than the amount of available system resources in the storagesystem (404) may cause overall system performance to degrade, and assuch, the I/O request (402) should be queued until sufficient systemresources are available to service the I/O request (402). In the examplemethod depicted in FIG. 4 , the I/O request (402) may be queued (412) inan entity-specific queue for the entity that is associated with the I/Orequest (402). Readers will appreciate that the storage system (404) maymaintain an entity-specific queue for each entity that may be associatedwith I/O requests that are serviced by the storage system (404).

Consider an example in which the storage system (404) services I/Orequests that are directed to one or ten volumes supported by thestorage system (404). In such an example, the storage system (404) maymaintain ten entity-specific queues, where a first entity-specific queueis used to store I/O requests directed to a first volume, a secondentity-specific queue is used to store I/O requests directed to a secondvolume, a third entity-specific queue is used to store I/O requestsdirected to a third volume, and so on. In such an example, when an I/Orequest (402) is received that is associated with a particular entity,if the amount of system resources required to service the I/O request(402) is greater than the amount of available system resources in thestorage system (404), the I/O request (402) will be queued (412) in theentity-specific queue for the entity that is associated with the I/Orequest (402).

The example method depicted in FIG. 4 also includes detecting (414) thatadditional system resources in the storage system (404) have becomeavailable. Detecting (414) that additional system resources in thestorage system (404) have become available may be carried out, forexample, by detecting that the storage system (404) has completed theexecution of one or more I/O requests. In such an example, the amount ofsystem resources within the storage system (404) that have becomeavailable may be a function of the type and number of I/O requests whoseexecution has completed.

Consider the example described above in which the storage system (404)is able to execute 1000 units of I/O requests in parallel while meetingthe predetermined performance threshold. In such an example, assume that100 read operations of 64 KB or less, 100 read operations of over 64 KBin size, 100 write operations of 64 KB or less, and 15 write operationsof over 64 KB in size are issued for execution by the storage system(404). In such an example, using the resource consumption table includedabove, the amount of available system resources in the storage system(404) would be 50 units of I/O requests. Further assume that executionof the 100 read operations of 64 KB or less subsequently completes,thereby indicating that additional system resources in the storagesystem (404) have become available. In such an example, using theresource consumption table included above, the amount of additionalsystem resources in the storage system (404) that have become availablewould be 100 units of I/O requests. Readers will appreciate that thestorage system (404) may track the amount of available system resourcesin the storage system (404) by initially setting the amount of availablesystem resources in the storage system (404) to a value that representsthe entire I/O processing capacity of the storage system (404), debitingthe value by the cost associated with an I/O request each time that anI/O request is issued to the storage system (404), and crediting thevalue by the cost associated with an I/O request each time thatexecution of a previously issued I/O request is completed.

The example method depicted in FIG. 4 also includes, responsive todetecting that additional system resources in the storage system (404)have become available, issuing (418) an I/O request from anentity-specific queue for an entity that has a highest priority amongentities with non-empty entity-specific queues. Readers will appreciatethat while the storage system (404) may maintain an entity-specificqueue for each entity that is associated with I/O requests that areserviced by the storage system (404), some entity-specific queues may beempty as no I/O requests associated with a particular entity may bestored in the entity-specific queue that is associated with theparticular entity. For those entities that have non-emptyentity-specific queues, however, an I/O request may be issued (418) forservicing by the storage system (404) from the entity-specific queue forthe entity that has a highest priority among entities with non-emptyentity-specific queues in response to detecting that additional systemresources in the storage system (404) have become available. Readerswill appreciate that an I/O request may only be issued (418) forservicing by the storage system (404) from the entity-specific queue forthe entity that has a highest priority among entities with non-emptyentity-specific queues, however, if the amount of available systemresources in the storage system (404) is equal to or greater than theamount of system resources required to service such an I/O request.

In the example method depicted in FIG. 4 , a priority for each entitythat utilizes the storage system (404) is determined based on the amountof I/O requests issued by the entity in a time-independent period and aweighted proportion of system resources designated for use by theentity. The time-independent period may be embodied, for example, as oneor more ‘generations’ of I/O requests, where each generation of I/Orequests may be equal to the amount of I/O requests that the storagesystem (404) may execute in parallel while meeting a predeterminedperformance threshold. Consider the example described above in which thestorage system (404) can execute 1000 units of I/O requests in parallelwhile meeting the predetermined performance threshold. In such anexample, a first generation of I/O requests may be defined as the first1000 units of I/O requests executed by the storage system (404), asecond generation of I/O requests may be defined as the second 1000units of I/O requests executed by the storage system (404), and so on.Readers will appreciate that one or more generations of I/O requests isa time-independent period, as a generation of I/O requests may onlycover a small period of time when the storage system (404) is receivinga relatively large number of I/O requests while another generation ofI/O requests may cover a much larger period of time when the storagesystem (404) is receiving a relatively small number of I/O requests.Stated differently, different generations of I/O requests may spandifferent lengths of time, thereby causing each period to betime-independent as two periods may cover different lengths of time. Forexample, a first generation of I/O requests may capture I/O requestsissued in a 1 second time period while a second generation of I/Orequests may capture I/O requests issued over a 100 ms time period.

In the example method depicted in FIG. 4 , a priority for each entitythat utilizes the storage system (404) is determined based not only onthe amount of I/O requests issued by the entity in a time-independentperiod, but the priority for each entity that utilizes the storagesystem (404) is also determined based and a weighted proportion ofsystem resources designated for use by the entity. The weightedproportion of system resources designated for use by the entity may beexpressed, for example, as a fractional proportion of system resourcesdesignated for use by the entity. For example, a first entity may have aweighted proportion of system resources that are designated for use bythe entity that is set to a value of 20% of system resources whereas asecond entity may have a weighted proportion of system resources thatare designated for use by the entity that is set to a value of 10% ofsystem resources. In an alternative embodiment, the weighted proportionof system resources designated for use by the entity may be expressed,for example, as a relative relationship between multiple entities. Forexample, a first entity may have a weighted proportion of systemresources that are designated for use by the entity that is set to avalue of twice the amount system resources that are designated for useby a second entity. Readers will appreciate that in other embodiments,the weighted proportion of system resources designated for use by eachentity may be expressed in other ways.

In the example method depicted in FIG. 4 , the weighted proportion ofsystem resources designated for use by the entity may be established ina variety of ways. For example, the weighted proportion of systemresources designated for use by each entity may be established throughthe use of a values provided by a system administrator or other user.Alternatively, the weighted proportion of system resources designatedfor use by each entity may be established through the use of one or moresystem configuration parameters, through the use of prioritiesassociated with various workloads, through the use of prioritiesassociated with various datasets, and so on. Readers will appreciatethat in other embodiments, the weighted proportion of system resourcesdesignated for use by the entity may be established in other ways.

In the example method depicted in FIG. 4 , determining a priority foreach entity that utilizes the storage system (404) based on the amountof I/O requests associated with the entity in a time-independent periodmay be carried out, for example, by assigning a highest priority to theentity that has the largest discrepancy between the weighted proportionof system resources designated for use by the entity and the amount ofI/O requests recently issued by the entity, by assigning a secondhighest priority to the entity that has the second largest discrepancybetween the weighted proportion of system resources designated for useby the entity and the amount of I/O requests recently issued by theentity, by assigning a third highest priority to the entity that has thethird largest discrepancy between the weighted proportion of systemresources designated for use by the entity and the amount of I/Orequests recently issued by the entity, and so on. Readers willappreciate that by taking into consideration the amount of I/O requeststhat are recently issued by the entity (e.g., through the use of acrediting/debiting system as described in other portions of thisapplication), costs associated with I/O requests issued during aplurality of previous time-independent periods may impact the priorityassociated with a particular entity. In an alternative embodiment, onlya predetermined number of priorities may exist and may be assigned toeach entity based on the weighted proportion of system resourcesdesignated for use by the entity and the amount of I/O requestsassociated with the entity in a time-independent period. For example, alowest priority may be assigned to all entities that issued an amount ofI/O requests during the time-independent period that was greater thantheir weighted proportion of system resources designated for use by theentity, and a highest priority may be assigned to all entities that didnot issue an amount of I/O requests during the time-independent periodthat was greater than their weighted proportion of system resourcesdesignated for use by the entity.

Consider the example described above in which the storage system (404)can execute 1000 units of I/O requests in parallel while meeting thepredetermined performance threshold. In such an example, assume that thetime-independent period is defined to include the most recent twogenerations of I/O requests serviced by the storage system (404), suchthat the time-independent period includes the most recent 2000 units ofI/O requests performed by the storage system (404). In this example,further assume that the storage system (404) services I/O requestsdirected to three distinct volumes (volume 1, volume 2, and volume 3),where in the most recent two generations of I/O requests serviced by thestorage system (404), 1200 units of I/O requests was directed to volume1, 600 units of I/O requests was directed to volume 2, and 200 units ofI/O requests was directed to volume 3. In such an example, assume thatthe weighted proportion of system resources designated for use by volume1 is 70% of total system resources, the weighted proportion of systemresources designated for use by volume 2 is 20% of total systemresources, and the weighted proportion of system resources designatedfor use by volume 3 is 10% of total system resources. In such anexample, volume 1 had utilized less than the weighted proportion ofsystem resources designated for use by volume 1, volume 2 had utilizedmore than the weighted proportion of system resources designated for useby volume 2, and volume 3 had utilized exactly the weighted proportionof system resources designated for use by volume 3. In such an example,a highest priority may be assigned to volume 1, a second highestpriority may be assigned to volume 3, and a lowest priority may beassigned to volume 2 based on the relative discrepancies between theweighted proportion of system resources designated for use by eachentity and the amount of I/O requests associated with each entity duringthe time-independent period.

For further explanation, FIG. 5 sets forth a flow chart illustrating anadditional example method for ensuring the appropriate utilization ofsystem resources using weighted workload based, time-independentscheduling according to embodiments of the present disclosure. Theexample method depicted in FIG. 5 is similar to the example methoddepicted in FIG. 4 , as the example method depicted in FIG. 5 alsoincludes receiving (406) an I/O request (402) associated with an entity,determining (408) whether an amount of system resources required toservice the I/O request (402) is greater than an amount of availablesystem resources in the storage system (404), issuing (420) the I/Orequest (402) to the storage system (404) in response to determiningthat the amount of system resources required to service the I/O requestis not (416) greater than the amount of available system resources inthe storage system (404), and in response to affirmatively (410)determining that the amount of system resources required to service theI/O request (402) is greater than the amount of available systemresources in the storage system (404): queueing (412) the I/O request(402) in an entity-specific queue for the entity that is associated withthe I/O request (402), detecting (414) that additional system resourcesin the storage system (404) have become available, and issuing (418) anI/O request from an entity-specific queue for an entity that has ahighest priority among entities with non-empty entity-specific queues inresponse to detecting that additional system resources in the storagesystem (404) have become available.

The example method depicted in FIG. 5 also includes determining (502) apriority for each entity with a non-empty entity-specific queue. In theexample method depicted in FIG. 5 , determining (502) a priority foreach entity with a non-empty entity-specific queue may be carried out,for example, by assigning a highest priority to the entity that has thelargest discrepancy between the weighted proportion of system resourcesdesignated for use by the entity and the amount of I/O requestsassociated with the entity during the time-independent period, byassigning a second highest priority to the entity that has the secondlargest discrepancy between the weighted proportion of system resourcesdesignated for use by the entity and the amount of I/O requestsassociated with the entity during the time-independent period, byassigning a third highest priority to the entity that has the thirdlargest discrepancy between the weighted proportion of system resourcesdesignated for use by the entity and the amount of I/O requestsassociated with the entity during the time-independent period, and soon. In an alternative embodiment, only a predetermined number ofpriorities may exist and may be assigned to each entity based on theweighted proportion of system resources designated for use by the entityand the amount of I/O requests associated with the entity in atime-independent period. For example, a lowest priority may be assignedto all entities that issued an amount of I/O requests during thetime-independent period that was greater than their weighted proportionof system resources designated for use by the entity, and a highestpriority may be assigned to all entities that did not issue an amount ofI/O requests during the time-independent period that was greater thantheir weighted proportion of system resources designated for use by theentity.

In the example method depicted in FIG. 5 , determining (502) a priorityfor each entity with a non-empty entity-specific queue can includedetermining (504) an amount of I/O requests that may be processed by thestorage system (404) in parallel. Determining (504) an amount of I/Orequests that may be processed by the storage system (404) in parallelmay be carried out, for example, through the use of one or more testsuites that issue I/O requests to the storage system (404).Alternatively, determining (504) an amount of I/O requests that may beprocessed by the storage system (404) in parallel may be carried out bymonitoring actual system performance during operation of the storagesystem (404) and identifying workload levels that cause systemperformance to degrade, as such a degradation in system performance maybe indicative that system capacity has been fully utilized. In such anexample, monitoring actual system performance during operation of thestorage system (404) may be carried out indefinitely as amount of I/Orequests that may be processed by the storage system (404) in parallelmay change over time in response to components within the storage system(404) aging, in response to the storage system (404) storing more data,and for a variety of other reasons.

In the example method depicted in FIG. 5 , determining (504) an amountof I/O requests that may be processed by the storage system (404) inparallel can include determining (506) the amount of I/O requests thatmay be processed by the storage system (404) in parallel while adheringto a response time requirement. Such a response time requirement mayspecify the maximum permissible amount of time that may lapse betweenthe time that an I/O request is issued to the storage system (404) andthe time that the storage system (404) indicates that the I/O requesthas been serviced. Readers will appreciate that in other embodiments,other or additional performance criteria may be taken into considerationas determining (504) an amount of I/O requests that may be processed bythe storage system (404) in parallel can potentially include determiningthe amount of I/O requests that may be processed by the storage system(404) in parallel while adhering to a read latency requirement,determining the amount of I/O requests that may be processed by thestorage system (404) in parallel while adhering to a write latencyrequirement, determining the amount of I/O requests that may beprocessed by the storage system (404) in parallel while adhering to anIOPS requirement, or determining the amount of I/O requests that may beprocessed by the storage system (404) in parallel while adhering toother requirements. In such an example, one or more of such performancecriteria may be taken into consideration when determining (504) anamount of I/O requests that may be processed by the storage system (404)in parallel.

In the example method depicted in FIG. 5 , determining (502) a priorityfor each entity with a non-empty entity-specific queue can also includeestablishing (508), in dependence upon the amount of I/O requests thatmay be processed by the storage system (404) in parallel, thetime-independent period. Establishing (508), in dependence upon theamount of I/O requests that may be processed by the storage system (404)in parallel, the time-independent period may be carried out byestablishing a time-independent period that includes one or moregenerations of I/O requests. In such an example, each generation of I/Orequests may be equal to the amount of I/O requests that the storagesystem (404) may process in parallel. Consider the example describedabove in which the storage system (404) can execute 1000 units of I/Orequests in parallel while meeting a predetermined performancethreshold. In such an example, a first generation of I/O requests may bedefined as the first 1000 units of I/O requests executed by the storagesystem (404), a second generation of I/O requests may be defined as thesecond 1000 units of I/O requests executed by the storage system (404),and so on. Readers will appreciate that one or more generations of I/Orequests is a time-independent period, as a generation of I/O requestsmay only cover a small period of time when the storage system (404) isreceiving a relatively large number of I/O requests while anothergeneration of I/O requests may cover a much larger period of time whenthe storage system (404) is receiving a relatively small number of I/Orequests. In the example method depicted in FIG. 5 , thetime-independent period can include an amount of most recently processedI/O requests that is equal to the amount of I/O requests that may beprocessed by the storage system in parallel, the time-independent periodcan include an amount of most recently processed I/O requests that isequal to an integer multiple of the amount of I/O requests that may beprocessed by the storage system in parallel, the time-independent periodcan include an amount of most recently processed I/O requests that isequal to an fractional portion of the amount of I/O requests that may beprocessed by the storage system in parallel, and so on.

In the example method depicted in FIG. 5 , determining (502) a priorityfor each entity with a non-empty entity-specific queue can also includedetermining (510) an amount of I/O requests processed for each entitywith a non-empty entity-specific queue during the time-independentperiod. Determining (510) the amount I/O requests processed for eachentity with a non-empty entity-specific queue during thetime-independent period may be carried out, for example, through the useof an I/O history maintained by one or more modules within the storagesystem. Such an I/O history may include information such as, a log ofI/O requests issued for processing on the storage array along with anidentifier of the entity that is associated with each I/O request, a logof I/O requests executed by the storage array along with an identifierof the entity that is associated with each I/O request, or otherinformation. Readers will appreciate that the ‘amount’ I/O requestsprocessed for each entity may be expressed in terms of the total costassociated with all I/O requests processed for each entity during thetime-independent period. In such an example, the total cost associatedwith all I/O requests processed for each entity during thetime-independent period may be calculated using information such as theresource consumption table described above. In such a way, all I/Orequests are not treated equally as some types of I/O requests requiremore system resources to execute than other types of I/O requests.

Consider an example in which a first entity was associated with 25 readoperations of 64 KB or less, 20 read operations of over 64 KB in size,10 write operations of 64 KB or less, and 5 write operations of over 64KB in size that were processed by the storage system (404) in thetime-independent period. In such an example, the amount of I/O requestsprocessed for the first entity during the time-independent period wouldbe determined (510) to be 165 units of I/O requests. In such an example,if a second entity was associated with 20 write operations of over 64 KBin size that were processed by the storage system (404) in thetime-independent period, the amount of I/O requests processed for thesecond entity during the time-independent period would be determined(510) to be 200 units of I/O requests, meaning that the amount of I/Orequests processed for the second entity during the time-independentperiod would be greater than the amount of I/O requests processed forthe first entity during the time-independent period, in spite of thefact that the number of I/O requests processed for the first entityduring the time-independent period was greater than the number of I/Orequests processed for the second entity during the time-independentperiod.

In the example method depicted in FIG. 5 , determining (502) a priorityfor each entity with a non-empty entity-specific queue can also includeassigning (512) priorities to each entity with a non-emptyentity-specific queue in dependence upon the amount I/O requestsprocessed for each entity with a non-empty entity-specific queue duringthe time-independent period and the weighted proportion of systemresources designated for use by the entity. Assigning (512) prioritiesto each entity with a non-empty entity-specific queue in dependence uponthe amount I/O requests processed for each entity with a non-emptyentity-specific queue during the time-independent period may be carriedout, for example, by assigning a highest priority to the entity that hasthe largest discrepancy between the weighted proportion of systemresources designated for use by the entity and the amount of I/Orequests associated with the entity during the time-independent period,by assigning a second highest priority to the entity that has the secondlargest discrepancy between the weighted proportion of system resourcesdesignated for use by the entity and the amount of I/O requestsassociated with the entity during the time-independent period, byassigning a third highest priority to the entity that has the thirdlargest discrepancy between the weighted proportion of system resourcesdesignated for use by the entity and the amount of I/O requestsassociated with the entity during the time-independent period, and soon. In an alternative embodiment, only a predetermined number ofpriorities may exist and may be assigned to each entity based on theweighted proportion of system resources designated for use by the entityand the amount of I/O requests associated with the entity in atime-independent period. For example, a lowest priority may be assignedto all entities that issued an amount of I/O requests during thetime-independent period that was greater than their weighted proportionof system resources designated for use by the entity, and a highestpriority may be assigned to all entities that did not issue an amount ofI/O requests during the time-independent period that was greater thantheir weighted proportion of system resources designated for use by theentity.

For further explanation, FIG. 6 sets forth a flow chart illustrating anadditional example method for ensuring the appropriate utilization ofsystem resources using weighted workload based, time-independentscheduling according to embodiments of the present disclosure. Theexample method depicted in FIG. 6 is similar to the example methodsdepicted in FIG. 4 and FIG. 5 , as the example method depicted in FIG. 5also includes receiving (406) an I/O request (402) associated with anentity, determining (408) whether an amount of system resources requiredto service the I/O request (402) is greater than an amount of availablesystem resources in the storage system (404), issuing (420) the I/Orequest (402) to the storage system (404) in response to determiningthat the amount of system resources required to service the I/O requestis not (416) greater than the amount of available system resources inthe storage system (404), and in response to affirmatively (410)determining that the amount of system resources required to service theI/O request (402) is greater than the amount of available systemresources in the storage system (404): queueing (412) the I/O request(402) in an entity-specific queue for the entity that is associated withthe I/O request (402), detecting (414) that additional system resourcesin the storage system (404) have become available, determining (502) apriority for each entity with a non-empty entity-specific queue, andissuing (418) an I/O request from an entity-specific queue for an entitythat has a highest priority among entities with non-emptyentity-specific queues in response to detecting that additional systemresources in the storage system (404) have become available.

In the example method depicted in FIG. 6 , determining (502) a priorityfor each entity with a non-empty entity-specific queue can includedetermining (602), in dependence upon the amount of I/O requests thatmay be processed by the storage system in parallel, a weighted share ofsystem resources for each entity. Determining (602) a weighted share ofsystem resources for each entity in dependence upon the amount of I/Orequests that may be processed by the storage system (404) in parallelmay be carried out, for example, by dividing the amount of I/O requeststhat may be processed by the storage system (404) in parallel inaccordance with the respective weighted proportion of system resourcesdesignated for use by each entity. Continuing with the examplesdescribed above, if the storage system (404) can execute 1000 units ofI/O requests in parallel and a first entity has a weighted proportion ofsystem resources that are designated for use by the first entity that isset to a value of 20% of system resources whereas a second entity has aweighted proportion of system resources that are designated for use bythe second entity that is set to a value of 10% of system resources, theweighted share of system resources for use by the first entity will be200 units of I/O requests per generation and the weighted share ofsystem resources for use by the second entity will be 100 units of I/Orequests per generation. Readers will appreciate that although FIG. 6describes determining (602) a weighted share of system resources foreach entity in dependence upon the amount of I/O requests that may beprocessed by the storage system (404) in parallel, the weighted share ofsystem resources for each entity may be determined (602) in dependenceupon the amount of I/O requests that may be processed by the storagesystem (404) in parallel while adhering to one or more performancecriteria.

In the example method depicted in FIG. 6 , determining (502) a priorityfor each entity with a non-empty entity-specific queue can also includeassigning (604) priorities to each entity with a non-emptyentity-specific queue in dependence upon the amount I/O requestsprocessed for each entity during the time-independent period in excessof the weighted share of system resources for each entity. Consider theexample described above in which the storage system (404) can execute1000 units of I/O requests in parallel while meeting a predeterminedperformance threshold. In such an example, assume that 3 entities areactively associated with incoming I/O requests. In this example, assumethat the weighted proportion of system resources that are designated foruse by the first entity that is set to a value of 50% of systemresources, the weighted proportion of system resources that aredesignated for use by the second entity that is set to a value of 30% ofsystem resources, and the weighted proportion of system resources thatare designated for use by the third entity that is set to a value of 20%of system resources. In such an example, assume that the first entitywas associated with 500 units of I/O requests that were processed duringthe time-independent period, the second entity was associated with 250units of I/O requests that were processed during the time-independentperiod, and the third entity was associated with 250 units of I/Orequests that were processed during the time-independent period. In theexample method depicted in FIG. 6 , assigning (604) priorities to eachentity with a non-empty entity-specific queue in dependence upon theamount I/O requests processed for each entity during thetime-independent period in excess of the weighted share of systemresources for each entity may be carried out, for example, by assigningthe lowest priority to the entity that most significantly exceeded itsweighted share, by assigning the second lowest priority to the entitythat exceeded its weighted share by the second largest amount, and soon. As such, in the example described above, the second entity would beassigned a highest priority, the first entity would be assigned a middlepriority, and the third entity would be assigned a lowest priority.

Readers will appreciate that the amount I/O requests processed for aparticular entity during the time-independent period may be in excess ofthe weighted share of system resources for such an entity because anyincoming I/O request (402) will be issued (420) to the storage system(404) in response to determining that the amount of system resourcesrequired to service the I/O request is not (416) greater than the amountof available system resources in the storage system (404), regardless ofwhich entity is associated with the I/O request.

For further explanation, FIG. 7 sets forth a flow chart illustrating anadditional example method for ensuring the appropriate utilization ofsystem resources using weighted workload based, time-independentscheduling according to embodiments of the present disclosure. Theexample method depicted in FIG. 7 is similar to the example methodsdepicted in FIG. 4 , FIG. 5 , and FIG. 6 , as the example methoddepicted in FIG. 7 also includes receiving (406) an I/O request (402)associated with an entity, determining (408) whether an amount of systemresources required to service the I/O request (402) is greater than anamount of available system resources in the storage system (404),issuing (420) the I/O request (402) to the storage system (404) inresponse to determining that the amount of system resources required toservice the I/O request is not (416) greater than the amount ofavailable system resources in the storage system (404), and in responseto affirmatively (410) determining that the amount of system resourcesrequired to service the I/O request (402) is greater than the amount ofavailable system resources in the storage system (404): queueing (412)the I/O request (402) in an entity-specific queue for the entity that isassociated with the I/O request (402), detecting (414) that additionalsystem resources in the storage system (404) have become available, andissuing (418) an I/O request from an entity-specific queue for an entitythat has a highest priority among entities with non-emptyentity-specific queues in response to detecting that additional systemresources in the storage system (404) have become available.

The example method depicted in FIG. 7 also includes determining (702),in dependence upon the amount of I/O requests that may be processed bythe storage system (404) in parallel, a weighted share of systemresources for each entity. Determining (702) a weighted share of systemresources for each entity in dependence upon the amount of I/O requeststhat may be processed by the storage system (404) in parallel may becarried out, for example, by dividing the amount of I/O requests thatmay be processed by the storage system (404) in parallel in accordancewith the respective weighted proportion of system resources designatedfor use by each entity. Continuing with the examples described above, ifthe storage system (404) can execute 1000 units of I/O requests inparallel and a first entity has a weighted proportion of systemresources that are designated for use by the first entity that is set toa value of 20% of system resources whereas a second entity has aweighted proportion of system resources that are designated for use bythe second entity that is set to a value of 10% of system resources, theweighted share of system resources for use by the first entity will be200 units of I/O requests per generation and the weighted share ofsystem resources for use by the second entity will be 100 units of I/Orequests per generation. Readers will appreciate that although FIG. 6describes determining (602) a weighted share of system resources foreach entity in dependence upon the amount of I/O requests that may beprocessed by the storage system (404) in parallel, the weighted share ofsystem resources for each entity may be determined (602) in dependenceupon the amount of I/O requests that may be processed by the storagesystem (404) in parallel while adhering to one or more performancecriteria.

The example method depicted in FIG. 7 further comprises, in response toissuing the I/O request (402), debiting (708) a resource utilizationbalance for the entity associated with the I/O request (402). Theresource utilization balance for the particular entity may represent arunning total of the extent to which the particular entity has utilizedits weighted share of system resources. The resource utilization balancemay initially be set to a value that includes the particular entity'sweighted share of system resources, and each time that the particularentity utilizes some system resources, the particular entity's resourceutilization balance may be debited (708) by an amount that is equal tothe amount of system resources that the particular entity consumed.Debiting (708) the resource utilization balance for the entityassociated with the I/O request (402) may be carried out, for example,by subtracting the amount of system resources required to service theI/O request (402) from resource utilization balance for the entity thatis associated with the I/O request (402). In such an example, bydebiting (708) the resource utilization balance for the entityassociated with the I/O request (402) in response to issuing the I/Orequest (402), the storage system (404) may track the extent to whicheach entity has utilized its weighted share of system resources.

Readers will appreciate that while the preceding paragraph describes anembodiment in which a resource utilization balance for the entityassociated with the I/O request (402) is debited (708) in response toissuing the I/O request (402), other embodiments are well within thescope of the present disclosure. For example, in some embodiments, eachentity may start with a balance of zero, accrue a charge each time theentity issues an I/O request, and then receive a credit at the end ofthe time-independent period. Readers will appreciate that othercrediting and debiting models may exist, all of which are well withinthe scope of the present disclosure.

The example method depicted in FIG. 7 also includes tracking (710), foreach entity, the amount I/O requests processed for each entity duringthe time-independent period. Tracking (710) the amount I/O requestsprocessed for each entity during the time-independent period may becarried out, for example, by summing up the amount of resources requiredto service each I/O request issued by each entity during thetime-independent period using information from a source such as theresource consumption table described above. Consider an example in whicha first entity was associated with 25 read operations of 64 KB or less,20 read operations of over 64 KB in size, 10 write operations of 64 KBor less, and 5 write operations of over 64 KB in size that wereprocessed by the storage system (404) in the time-independent period. Insuch an example, the amount of I/O requests processed for the firstentity during the time-independent period would be 165 units of I/Orequests.

The example method depicted in FIG. 7 also includes crediting (712) theresource utilization balance for each entity with the weighted share ofsystem resources for each entity upon the expiration of thetime-independent period. Readers will appreciate that by crediting (712)the resource utilization balance for each entity with the weighted shareof system resources for each entity upon the expiration of thetime-independent period, rather than crediting the resource utilizationbalance for an entity associated with an I/O request when the I/Orequest completes, entities that use more than their weighted share ofsystem resources can be tracked such that entities that use more thantheir weighted share of system resources may be given lower prioritywhen system utilization reaches system capacity.

Consider the example described above in which the storage system (404)can execute 1000 units of I/O requests in parallel while meeting apredetermined performance threshold, three entities are actively issuingI/O requests to the storage system, the weighted proportion of systemresources that are designated for use by the first entity that is set toa value of 50% of system resources (e.g., 500 units of I/O requests pertime-independent period), the weighted proportion of system resourcesthat are designated for use by the second entity that is set to a valueof 30% of system resources (e.g., 300 units of I/O requests pertime-independent period), and the weighted proportion of systemresources that are designated for use by the third entity that is set toa value of 20% of system resources (e.g., 200 units of I/O requests pertime-independent period). In such an example, assume that in the currenttime-independent period, the third entity caused 900 units of I/Orequests issued, resulting in the storage system (404) hitting its fullcapacity and further resulting in the queueing of I/O requests. In suchan example, because the resource utilization balance for the thirdentity is debited (708) as each I/O request is issued, the third entitywould quickly develop a negative resource utilization balance, therebyidentifying the third entity as an entity that has utilized systemresources in excess of its weighted share. As the execution of such I/Orequests completes, if the resource utilization balance for the thirdentity were to be credited with the amount of system resources requiredto service each I/O request as each I/O request completes, the thirdentity would quickly return to a state where it has a non-negativeresource utilization balance and it is not characterized as havingutilized system resources in excess of its weighted share, in spite ofthe fact that the performance of I/O requests associated with otherentities suffered in large part because the third entity issued such alarge amount of I/O requests. Rather than creating a situation where anentity can quickly be absolved of such resource overutilization, by onlycrediting (712) the resource utilization balance for each entity withthe weighted share of system resources for each entity upon theexpiration of the time-independent period, the entity must cease overutilizing system resources in order to return to a state where it is notcharacterized as having utilized system resources in excess of itsweighted share.

The example method depicted in FIG. 7 also includes determining (704)the amount of system resources required to service the I/O request(402). Determining (704) the amount of system resources required toservice the I/O request (402) may be carried out, for example, throughthe use of a resource consumption table or other information source thatassociates various types of I/O requests with the amount of systemresources required to service each type of I/O request. The resourceconsumption table or other information source that associates varioustypes of I/O requests with the amount of system resources required toservice each type of I/O request may be generated, for example, throughthe use of a test suite, by observing and analyzing actual systemperformance over the lifespan of the storage system (404), or in otherways.

The example method depicted in FIG. 7 also includes determining (706)the amount of available system resources in the storage system (404).The amount of available system resources in the storage system (404) mayrepresent the portion of total system capacity that is not currently inuse. Continuing with the example described above in which the storagesystem (404) would be able to execute 1000 units of I/O requests inparallel while meeting the predetermined performance threshold, assumethat the storage system (404) is currently executing 100 read operationsof 64 KB or less, 100 read operations of over 64 KB in size, 100 writeoperations of 64 KB or less, and 15 write operations of over 64 KB insize. Using the resource consumption table included above, the 100 readoperations of 64 KB or less would consume 100 units of I/O requests, the100 read operations of over 64 KB in size would consume 200 units of I/Orequests, the 100 write operations of 64 KB or less would consume 500units of I/O requests, and the 15 write operations of over 64 KB in sizewould consume 150 units of I/O requests. As such, the amount ofavailable system resources in the storage system (404) would be 50 unitsof I/O requests, as 950 units of I/O requests are currently beingconsumed by the I/O requests currently executing on the storage system(404). In the example method depicted in FIG. 7 , determining (706) theamount of available system resources in the storage system (404) may becarried out, for example, by initially setting the amount of availablesystem resources in the storage system (404) to a value that representsthe amount of I/O requests that the storage can process in parallel(possibly even while adhering to one or more performance criteria). Eachtime an I/O request is issued for servicing by the storage system (404),the amount of available system resources in the storage system (404) maybe debited by an amount that is equal to the amount of system resourcesrequired to service the I/O request. Likewise, each time the storagesystem (404) finishes servicing an I/O request, the amount of availablesystem resources in the storage system (404) may be credited by anamount that is equal to the amount of system resources required toservice the I/O request.

For further explanation, FIG. 8 sets forth a flow chart illustrating anadditional example method for ensuring the appropriate utilization ofsystem resources using weighted workload based, time-independentscheduling according to embodiments of the present disclosure. Theexample method depicted in FIG. 8 may be carried out, for example, by astorage system that is identical to or similar to the storage systemsdescribed above with reference to FIGS. 1-3 , as the storage system(404) can include storage devices (422, 424, 426) as well as many of theother components described in the previous figures.

The example method depicted in FIG. 8 includes determining (802) whetheran amount of available system resources in the storage system (802) hasreached a predetermined reservation threshold. The predeterminedreservation threshold can represent an amount of system resources whoseusage should be restricted, so that some portion of the system resourcegenerally remains available. Consider an example in which a systemresource such an NVRAM device, as described above, is associated with apredetermined reservation threshold of 10%. As described above, such anNVRAM device may be utilized as a quickly accessible buffer for datadestined to be written to one or the storage devices (816, 818, 820) inthe storage system (802). By utilizing the NVRAM device in such a way,the write latency experienced by users of the storage system (802) maybe significantly improved relative to storage systems that do notinclude such NVRAM devices. The write latency experienced by users ofthe storage system (802) may be significantly improved relative tostorage systems that do not include such a NVRAM devices because astorage array controller may send an acknowledgment to the user of thestorage system (802) indicating that a write request has been servicedonce the data associated with the write request has been written to oneor more of the NVRAM devices, even if the data associated with the writerequest has not yet been written to any of the storage devices (816,818, 820). Readers will appreciate that if the NVRAM device becomescompletely full, system performance may suffer significantly. As such,it may be prudent to restrict access to some portion of the NVRAM devicethrough the use of a predetermined reservation threshold.

In the example method depicted in FIG. 8 , determining (802) whether anamount of available system resources in the storage system (802) hasreached a predetermined reservation threshold may be carried out, forexample, by comparing the total amount a particular system resource thatexists in the storage system (802) to the total amount the particularsystem resource that is currently available, by comparing the totalamount a particular system resource that exists in the storage system(802) to the total amount the particular system resource that iscurrently in use, or in other ways. Continuing with the example in whicha system resource such a NVRAM device is associated with a predeterminedreservation threshold of 10%, if the total capacity of the NVRAM deviceis 1 TB and the amount of free space in the NVRAM device is 100 GB, theamount of available write buffer (822) resources in the storage system(802) has reached the predetermined reservation threshold.

The example method depicted in FIG. 8 also includes, in response toaffirmatively (806) determining that the amount of available systemresources in the storage system (802) has reached the predeterminedreservation threshold, determining (808) whether one or more entities inthe storage system (802) have utilized system resources in excess oftheir weighted share by a predetermined threshold during one or moretime-independent periods. In the example method depicted in FIG. 8 , theweighted share of a particular system resource for each entity that isassociated with incoming I/O requests may be determined by dividing thetotal amount of the particular system resource that is in the storagesystem (802) in accordance with the respective weighted proportion ofsystem resources designated for use by each entity. Continuing with theexample described above in which a system resource such a write bufferdevice (822) has a total capacity of 1 TB, assume that there are threeentities are actively issuing I/O requests to the storage system and theweighted proportion of system resources that are designated for use bythe first entity that is set to a value of 50% of system resources, theweighted proportion of system resources that are designated for use bythe second entity that is set to a value of 30% of system resources, andthe weighted proportion of system resources that are designated for useby the third entity that is set to a value of 20% of system resources.In such an example, determining (808) whether one or more entities inthe storage system (802) have utilized system resources in excess oftheir weighted share by a predetermined threshold during one or moretime-independent periods may be carried out, for example, by using acrediting/debiting mechanism as described above.

The example method depicted in FIG. 8 also includes, in response toaffirmatively (810) determining that one or more entities in the storagesystem (802) have utilized system resources in excess of their weightedshare by the predetermined threshold during the time-independent period,limiting (812) the one or more entities from issuing additional I/Orequests to the storage system (802). In the example method depicted inFIG. 8 , limiting (812) the one or more entities from issuing additionalI/O requests to the storage system (802) may be carried out, forexample, by reducing the amount of additional I/O requests associatedwith an entity that used more than its weighted share of systemresources that may be issued to the storage system (802). The one ormore entities may be limited (812) from issuing additional I/O requeststo the storage system (802), for example, until a resource utilizationbalance as described above is restored to an acceptable level throughthe use of a debiting and crediting system described above, until theamount of available system resources in the storage system (802) hasfallen below the predetermined reservation threshold, or until theoccurrence of some other event.

In the example method depicted in FIG. 8 , limiting (812) the one ormore entities from issuing additional I/O requests to the storage system(802) can include blocking (814) the one or more entities from issuingadditional I/O requests to the storage system (802). By blocking (814)the one or more entities from issuing additional I/O requests to thestorage system (802), the one or more entities that have utilized morethan their weighted share of system resources may be entirely prohibitedfrom having any additional I/O requests associated with such an entityissued to the storage system (802). The one or more entities may beblocked (814) from issuing additional I/O requests to the storage system(802), for example, until a resource utilization balance as describedabove is restored to an acceptable level through the use of a debitingand crediting system described above, until the amount of availablesystem resources in the storage system (802) has fallen below thepredetermined reservation threshold, or until the occurrence of someother event.

For further explanation, FIG. 9 sets forth a flow chart illustrating anadditional example method for ensuring the appropriate utilization ofsystem resources using weighted workload based, time-independentscheduling according to embodiments of the present disclosure. Theexample method depicted in FIG. 9 is similar to the example methoddepicted in FIG. 8 , as the example method depicted in FIG. 9 alsoincludes determining (802) whether an amount of available systemresources in the storage system (802) has reached a predeterminedreservation threshold, determining (808) whether one or more entities inthe storage system (802) have utilized system resources in excess oftheir weighted share by a predetermined threshold during one or moretime-independent periods, and limiting (812) the one or more entitiesfrom issuing additional I/O requests to the storage system (802).

The example method depicted in FIG. 9 also includes determining (902) anamount of I/O requests that may be processed by the storage system (802)in parallel. Determining (902) an amount of I/O requests that may beprocessed by the storage system (802) in parallel may be carried out,for example, through the use of one or more test suites that issue I/Orequests to the storage system (802). Alternatively, determining (902)an amount of I/O requests that may be processed by the storage system(802) in parallel may be carried out by monitoring actual systemperformance during operation of the storage system (802) and identifyingworkload levels that cause system performance to degrade, as such adegradation in system performance may be indicative that system capacityhas been fully utilized. In such an example, monitoring actual systemperformance during operation of the storage system (802) may be carriedout indefinitely as amount of I/O requests that may be processed by thestorage system (802) in parallel may change over time in response tocomponents within the storage system (802) aging, in response to thestorage system (802) storing more data, and for a variety of otherreasons.

In the example method depicted in FIG. 9 , determining (902) an amountof I/O requests that may be processed by the storage system (802) inparallel can include determining (904) the amount of I/O requests thatmay be processed by the storage system (802) in parallel while adheringto a performance requirement. Such a performance requirement mayspecify, for example, the maximum permissible amount of time that maylapse between the time that an I/O request is issued to the storagesystem (802) and the time that the storage system (802) indicates thatthe I/O request has been serviced. Readers will appreciate that in otherembodiments, other or additional performance criteria may be taken intoconsideration as determining (904) an amount of I/O requests that may beprocessed by the storage system (802) in parallel while adhering to aperformance requirement can potentially include determining the amountof I/O requests that may be processed by the storage system (802) inparallel while adhering to a read latency requirement, determining theamount of I/O requests that may be processed by the storage system (802)in parallel while adhering to a write latency requirement, determiningthe amount of I/O requests that may be processed by the storage system(802) in parallel while adhering to an IOPS requirement, or determiningthe amount of I/O requests that may be processed by the storage system(802) in parallel while adhering to other requirements. In such anexample, one or more of such performance criteria may be taken intoconsideration when determining (904) an amount of I/O requests that maybe processed by the storage system (802) in parallel while adhering to aperformance requirement.

The example method depicted in FIG. 9 also includes establishing (906),in dependence upon the amount of I/O requests that may be processed bythe storage system (802) in parallel, the time-independent period.Establishing (906), in dependence upon the amount of I/O requests thatmay be processed by the storage system (802) in parallel, thetime-independent period may be carried out by establishing atime-independent period that includes one or more generations of I/Orequests. In such an example, each generation of I/O requests may beequal to the amount of I/O requests that the storage system (802) mayprocess in parallel. Consider the example described above in which thestorage system (802) can execute 1000 units of I/O requests in parallelwhile meeting a predetermined performance threshold. In such an example,a first generation of I/O requests may be defined as the first 1000units of I/O requests executed by the storage system (802), a secondgeneration of I/O requests may be defined as the second 1000 units ofI/O requests executed by the storage system (802), and so on. Readerswill appreciate that one or more generations of I/O requests is atime-independent period, as a generation of I/O requests may only covera small period of time when the storage system (802) is receiving arelatively large number of I/O requests while another generation of I/Orequests may cover a much larger period of time when the storage system(802) is receiving a relatively small number of I/O requests. In theexample method depicted in FIG. 9 , the time-independent period caninclude an amount of most recently processed I/O requests that is afunction of the amount of I/O requests that may be processed by thestorage system (802) in parallel as the time-independent period caninclude an amount of most recently processed I/O requests that is equalto an integer multiple of the amount of I/O requests that may beprocessed by the storage system in parallel, the time-independent periodcan include an amount of most recently processed I/O requests that isequal to an fractional portion of the amount of I/O requests that may beprocessed by the storage system in parallel, and so on.

For further explanation, FIG. 10 sets forth a flow chart illustrating anadditional example method for ensuring the appropriate utilization ofsystem resources using weighted workload based, time-independentscheduling according to embodiments of the present disclosure. Theexample method depicted in FIG. 10 is similar to the example methoddepicted in FIG. 8 , as the example method depicted in FIG. 10 alsoincludes determining (802) whether an amount of available systemresources in the storage system (802) has reached a predeterminedreservation threshold, determining (808) whether one or more entities inthe storage system (802) have utilized system resources in excess oftheir weighted share by a predetermined threshold during one or moretime-independent periods, and limiting (812) the one or more entitiesfrom issuing additional I/O requests to the storage system (802).

The example method depicted in FIG. 10 also includes determining (1002),in dependence upon the amount of I/O requests that may be processed bythe storage system (802) in parallel, a weighted share of systemresources for each entity. Determining (1002) a weighted share of systemresources for each entity in dependence upon the amount of I/O requeststhat may be processed by the storage system (802) in parallel may becarried out, for example, by determining how many entities are activelyassociated with incoming I/O requests and by dividing the amount of I/Orequests that may be processed by the storage system (404) in parallelin accordance with the respective weighted proportion of systemresources designated for use by each entity. In some embodiments, theweighted share of system resources for each entity may be determined byonly taking into consideration those entities that are activelyassociated with incoming I/O requests. A particular entity may be deemedto be ‘actively’ associated with incoming I/O requests, for example, ifany I/O requests that are associated with the particular entity havebeen received during a predetermined number of most recent I/Ogenerations. Readers will appreciate that although FIG. 10 describesdetermining (1002) a weighted share of system resources for each entityin dependence upon the amount of I/O requests that may be processed bythe storage system (802) in parallel, the weighted share of systemresources for each entity may be determined (1002) in dependence uponthe amount of I/O requests that may be processed by the storage system(802) in parallel while adhering to one or more performance criteria.

The example method depicted in FIG. 10 also includes determining (1004)whether an additional time-independent period has expired since the oneor more entities were limited from issuing additional I/O requests tothe storage system (802). In the example method depicted in FIG. 10 ,determining (1004) whether an additional time-independent period hasexpired since the one or more entities were limited from issuingadditional I/O requests to the storage system (802) may be carried outby tracking the amount of I/O requests that were issued since the one ormore entities were limited from issuing additional I/O requests to thestorage system (802). In an example in which the time-independent periodis a function of the amount of I/O requests that are included in ageneration of I/O requests, an additional time-independent period hasexpired once the amount of I/O requests that were issued since the oneor more entities were limited from issuing additional I/O requests tothe storage system (802) has reached the amount of the amount of I/Orequests that are included in the time-independent period.

The example method depicted in in FIG. 10 also includes, in response toaffirmatively (1006) determining that the additional time-independentperiod has expired since the one or more entities were blocked fromissuing additional I/O requests to the storage system (802), crediting(1008) the one or more entities with at least a portion of its weightedshare of system resources. Crediting (1008) the one or more entitieswith at least a portion of its weighted share of system resources may becarried out, for example, through the use of a resource utilizationbudget or similar mechanism that is maintained for each entity that isassociated with I/O requests that are serviced by the storage system(802).

For further explanation, FIG. 11 sets forth a flow chart illustrating anadditional example method for ensuring the appropriate utilization ofsystem resources using weighted workload based, time-independentscheduling according to embodiments of the present disclosure. Theexample method depicted in FIG. 11 is similar to the example methoddepicted in FIG. 8 , as the example method depicted in FIG. 11 alsoincludes determining (802) whether an amount of available systemresources in the storage system (802) has reached a predeterminedreservation threshold, determining (808) whether one or more entities inthe storage system (802) have utilized system resources in excess oftheir weighted share by a predetermined threshold during one or moretime-independent periods, and limiting (812) the one or more entitiesfrom issuing additional I/O requests to the storage system (802).

The example method depicted in FIG. 11 also includes determining (1102)whether the amount of available system resources in the storage system(802) has become larger than the predetermined reservation threshold.Determining (1102) whether the amount of available system resources inthe storage system (802) has become larger than the predeterminedreservation threshold may be carried out, for example, by comparing thetotal amount a particular system resource that exists in the storagesystem (802) to the total amount the particular system resource that iscurrently available. Continuing with the example in which a systemresource such a write buffer device (822) is associated with apredetermined reservation threshold of 10%, if the total capacity of thewrite buffer device (822) is 1 TB, the amount of available systemresources in the storage system (802) will have become larger than thepredetermined reservation threshold when the amount of free space in thewrite buffer device (822) becomes larger than 100 TB.

The example method depicted in FIG. 11 also includes, in response toaffirmatively (1104) determining that the amount of available systemresources in the storage system (802) has become larger than thepredetermined reservation threshold, enabling (1106) the one or moreentities to issue additional I/O requests to the storage system (804).In the example method depicted in FIG. 11 , enabling (1106) the one ormore entities to issue additional I/O requests to the storage system(804) may be carried out by removing any limitations that werepreviously in place for entities one or more entities in the storagesystem (802) that have utilized system resources in excess of theirweighted share and were previously limited (812) from issuing additionalI/O requests to the storage system (802).

For further explanation, FIG. 12 sets forth a flow chart illustrating anadditional example method for ensuring the appropriate utilization ofsystem resources using weighted workload based, time-independentscheduling according to embodiments of the present disclosure. Theexample method depicted in FIG. 12 may be carried out, for example, by astorage system that is identical to or similar to the storage systemsdescribed above with reference to FIGS. 1-3 as well as many of the othercomponents described in the previous figures.

The example method depicted in FIG. 12 also includes determining (1204)whether an amount of system resource utilization in the storage system(1202) has reached a predetermined utilization threshold. Thepredetermined utilization threshold can represent an amount of systemresources that may be used before restrictions are put in place, so thatsome portion of the system resource generally remains available.Consider an example in which a system resource such a write bufferdevice (1222), as described above with reference to FIG. 1 , isassociated with a predetermined utilization threshold of 90%. Asdescribed above, such a write buffer device (1222) may be utilized as aquickly accessible buffer for data destined to be written to one or thestorage devices (1216, 1218, 1220) in the storage system (1202). Byutilizing the write buffer device (1222) in such a way, the writelatency experienced by users of the storage system (1202) may besignificantly improved relative to storage systems that do not includesuch write buffer devices (1222). The write latency experienced by usersof the storage system (1202) may be significantly improved relative tostorage systems that do not include such a write buffer device (1202)because a storage array controller may send an acknowledgment to theuser of the storage system (1202) indicating that a write request hasbeen serviced once the data associated with the write request has beenwritten to one or the write buffer devices (1222), even if the dataassociated with the write request has not yet been written to any of thestorage devices (1216, 1218, 1220). Readers will appreciate that if thewrite buffer device (1222) becomes completely full, system performancemay suffer significantly. As such, it may be prudent to restrict accessto some portion of the write buffer device (1222) through the use of apredetermined utilization threshold.

In the example method depicted in FIG. 12 , determining (1204) whetheran amount of system resource utilization in the storage system (1202)has reached a predetermined utilization threshold may be carried out,for example, by comparing the total amount a particular system resourcethat exists in the storage system (1202) to the total amount theparticular system resource that is currently available, comparing thetotal amount a particular system resource that exists in the storagesystem (1202) to the total amount the particular system resource that iscurrently in use, or in other ways. Continuing with the example in whicha system resource such a write buffer device (1222) is associated with apredetermined utilization threshold of 90%, if the total capacity of thewrite buffer device (822) is 1 TB and the amount of free space in thewrite buffer device is 100 GB, the amount of write buffer (1222)utilization has reached the predetermined utilization threshold.

The example method depicted in FIG. 12 also includes, in response toaffirmatively 1206) determining that the amount of system resourceutilization in the storage system (1202) has reached a predeterminedutilization threshold, determining (1208) whether one or more entitiesin the storage system have utilized system resources in excess of theirweighted share by a predetermined threshold during a time-independentperiod. In the example method depicted in FIG. 12 , the weighted shareof a particular system resource for each entity that is associated withincoming I/O requests may be determined as described above.

In the example method depicted in FIG. 12 , determining (1208) whetherone or more entities in the storage system (1202) have utilized systemresources in excess of their weighted share by a predetermined thresholdduring one or more time-independent periods may be carried out, forexample, by comparing the amount of a particular system resource that isutilized by each entity to the weighted share of such a resource foreach entity as described above. In some embodiments, the predeterminedthreshold may be set to a non-zero value to allow for some level ofresource utilization in excess of an entity's weighted share, and inother embodiments the predetermined threshold may be set of a value ofzero.

The example method depicted in FIG. 12 also includes, in response toaffirmatively (1210) determining that one or more entities in thestorage system (1202) have utilized system resources in excess of theirweighted share by the predetermined threshold during thetime-independent period, freezing (1212), at least partially, an amountby which the one or more entities in the storage system (1202) haveutilized system resources in excess of their weighted share. Freezing(1212), at least partially, an amount by which the one or more entitiesin the storage system (1202) have utilized system resources in excess oftheir weighted share may be carried out through the use of a resourceutilization budget or similar mechanism that is maintained for eachentity that is associated with I/O requests that are serviced by thestorage system (1202). In such an example, when an I/O request that isassociated with a particular entity is issued to the storage system(1202), the resource utilization budget for the particular entity may bedebited by an amount that is equal to the amount of system resourcesrequired to service the I/O operation. If a particular entity utilizedsystem resources in excess of their weighted share the entity mayultimately be blocked from issuing additional I/O requests to thestorage system (1202). Readers will appreciate that in some embodiments,as the resource utilization budget for entities are credited (e.g., uponthe expiration of a time-independent period), crediting the resourceutilization budget for an entity that is blocked from issuing additionalI/O requests to the storage system (1202) may have the unintendedconsequence of making an over-consuming entity appear to be an entitythat is not consuming more than its weighted share of system resourcesby virtue of the entity being blocked from issuing additional I/Orequests to the storage system (1202). To avoid this outcome, in theexample method depicted in FIG. 12 , the amount by which the one or moreentities in the storage system (1202) have utilized system resources inexcess of their weighted share may be at least partially frozen (1212).Freezing (1212), at least partially, an amount by which the one or moreentities in the storage system (1202) have utilized system resources inexcess of their weighted share may be carried out, for example, bydecreasing the extent to which the resource utilization budget for anentity that is blocked from issuing additional I/O requests to thestorage system (1202) is credited while the entity is blocked fromissuing additional I/O requests to the storage system (1202).

In the example method depicted in FIG. 12 , freezing (1212), at leastpartially, an amount by which the one or more entities in the storagesystem (1202) have utilized system resources in excess of their weightedshare can include freezing (1214) the amount by which the one or moreentities in the storage system (1202) have utilized system resources inexcess of their weighted share. In the example method depicted in FIG.12 , freezing (1214) the amount by which the one or more entities in thestorage system (1202) have utilized system resources in excess of theirweighted share may be carried out, for example, by ceasing to credit theresource utilization budget for an entity that is blocked from issuingadditional I/O requests to the storage system (1202) while the entity isblocked from issuing additional I/O requests to the storage system(1202).

For further explanation, FIG. 13 sets forth a flow chart illustrating anadditional example method for ensuring the appropriate utilization ofsystem resources using weighted workload based, time-independentscheduling according to embodiments of the present disclosure. Theexample method depicted in FIG. 13 is similar to the example methoddepicted in FIG. 12 , as the example method depicted in FIG. 13 alsoincludes determining (1204) whether an amount of system resourceutilization in the storage system (1202) has reached a predeterminedutilization threshold, determining (1208) whether one or more entitiesin the storage system have utilized system resources in excess of theirweighted share by a predetermined threshold during a time-independentperiod in response to affirmatively (1206) determining that the amountof system resource utilization in the storage system (1202) has reacheda predetermined utilization threshold, and freezing (1212), at leastpartially, an amount by which the one or more entities in the storagesystem (1202) have utilized system resources in excess of their weightedshare in response to affirmatively (1210) determining that one or moreentities in the storage system (1202) have utilized system resources inexcess of their weighted share by the predetermined threshold during thetime-independent period.

The example method depicted in FIG. 13 also includes, in response toaffirmatively (1210) determining that one or more entities in thestorage system (1202) have utilized system resources in excess of theirweighted share by the predetermined threshold during thetime-independent period, blocking (1302) the one or more entities fromissuing additional I/O requests to the storage system (1202). Byblocking (1302) the one or more entities from issuing additional I/Orequests to the storage system (1202), the one or more entities thathave utilized more than their weighted share of system resources may beentirely prohibited from having any additional I/O requests associatedwith such an entity issued to the storage system (1202). The one or moreentities may be blocked (1302) from issuing additional I/O requests tothe storage system (1202), for example, until a resource utilizationbalance as described above is restored to an acceptable level throughthe use of a debiting and crediting system described above, until theamount of available system resources in the storage system (1202) hasfallen below the predetermined reservation threshold, or until theoccurrence of some other event. Readers will appreciate that in otherembodiments, the one or more entities that have utilized more than theirweighted share of system resources may be only partially prohibited(i.e., limited) from having any additional I/O requests associated withsuch an entity issued to the storage system (1202).

The example method depicted in FIG. 13 also includes determining (1304)whether the amount of system resource utilization in the storage system(1202) has fallen below the predetermined utilization threshold.Determining (1304) whether the amount of system resource utilization inthe storage system (1202) has fallen below the predetermined utilizationthreshold may be carried out, for example, by comparing the total amounta particular system resource that exists in the storage system (1202) tothe total amount the particular system resource that is currentlyavailable, by comparing the total amount a particular system resourcethat exists in the storage system (1202) to the total amount theparticular system resource that is currently in use, or in other ways.Continuing with the example in which a system resource such a writebuffer device (1222) is associated with a predetermined utilizationthreshold of 90%, if the total capacity of the write buffer device(1222) is 1 TB, the amount of system resource utilization in the storagesystem (1202) will have fallen below the predetermined utilizationthreshold when the amount of free space in the write buffer device(1222) becomes larger than 100 GB.

The example method depicted in FIG. 13 also includes, in response toaffirmatively (1310) determining that one or more entities in thestorage system (1202) have utilized system resources in excess of theirweighted share by the predetermined threshold during thetime-independent period, unfreezing (1306), at least partially, theamount by which the one or more entities in the storage system (1202)have utilized system resources in excess of their weighted share.Unfreezing (1306), at least partially, the amount by which the one ormore entities in the storage system (1202) have utilized systemresources in excess of their weighted share may be carried out throughthe use of a resource utilization budget or similar mechanism that ismaintained for each entity that is associated with I/O requests that areserviced by the storage system (1202). In such an example, when an I/Orequest that is associated with a particular entity is issued to thestorage system (1202), the resource utilization budget for theparticular entity may be debited by an amount that is equal to theamount of system resources required to service the I/O operation. In theexample method depicted in FIG. 12 , at least partially unfreezing(1306) the amount by which the one or more entities in the storagesystem (1202) have utilized system resources in excess of their weightedshare may be carried out, for example, by enabling the resourceutilization budget for an entity that is blocked from issuing additionalI/O requests to the storage system (1202) to be credited.

In the example method depicted in FIG. 13 , at least partiallyunfreezing (1306) the amount by which the one or more entities in thestorage system (1202) have utilized system resources in excess of theirweighted share can include determining (1308) whether an additionaltime-independent period has expired since the amount by which the one ormore entities in the storage system (1202) have utilized systemresources in excess of their weighted share was at least partiallyfrozen (1212). In the example method depicted in FIG. 13 , in responseto affirmatively (1310) determining that the additional time-independentperiod has expired since the amount by which the one or more entities inthe storage system (1202) have utilized system resources in excess oftheir weighted share was at least partially frozen (1212), crediting(1312) the one or more entities with at least a portion of its weightedshare of system resources.

For further explanation, FIG. 14 sets forth a flow chart illustrating anadditional example method for ensuring the appropriate utilization ofsystem resources using weighted workload based, time-independentscheduling according to embodiments of the present disclosure. Theexample method depicted in FIG. 14 is similar to the example methoddepicted in FIG. 12 , as the example method depicted in FIG. 14 alsoincludes determining (1204) whether an amount of system resourceutilization in the storage system (1202) has reached a predeterminedutilization threshold, determining (1208) whether one or more entitiesin the storage system have utilized system resources in excess of theirweighted share by a predetermined threshold during a time-independentperiod in response to affirmatively (1206) determining that the amountof system resource utilization in the storage system (1202) has reacheda predetermined utilization threshold, and freezing (1212), at leastpartially, an amount by which the one or more entities in the storagesystem (1202) have utilized system resources in excess of their weightedshare in response to affirmatively (1210) determining that one or moreentities in the storage system (1202) have utilized system resources inexcess of their weighted share by the predetermined threshold during thetime-independent period.

The example method depicted in FIG. 14 also includes determining (1402)an amount of I/O requests that may be processed by the storage system(1202) in parallel. Determining (1402) an amount of I/O requests thatmay be processed by the storage system (1202) in parallel may be carriedout, for example, through the use of one or more test suites that issueI/O requests to the storage system (1202). Alternatively, determining(1402) an amount of I/O requests that may be processed by the storagesystem (1202) in parallel may be carried out by monitoring actual systemperformance during operation of the storage system (1202) andidentifying workload levels that cause system performance to degrade, assuch a degradation in system performance may be indicative that systemcapacity has been fully utilized. In such an example, monitoring actualsystem performance during operation of the storage system (1202) may becarried out indefinitely as amount of I/O requests that may be processedby the storage system (1202) in parallel may change over time inresponse to components within the storage system (1202) aging, inresponse to the storage system (1202) storing more data, and for avariety of other reasons.

Although not expressly depicted in FIG. 14 , readers will appreciatethat determining (1402) an amount of I/O requests that may be processedby the storage system (1202) in parallel can include determining theamount of I/O requests that may be processed by the storage system(1202) in parallel while adhering to a performance requirement. Such aperformance requirement may specify, for example, the maximumpermissible amount of time that may lapse between the time that an I/Orequest is issued to the storage system (1202) and the time that thestorage system (1202) indicates that the I/O request has been serviced.Readers will appreciate that in other embodiments, other or additionalperformance criteria may be taken into consideration as determining anamount of I/O requests that may be processed by the storage system(1202) in parallel while adhering to a performance requirement canpotentially include determining the amount of I/O requests that may beprocessed by the storage system (1202) in parallel while adhering to aread latency requirement, determining the amount of I/O requests thatmay be processed by the storage system (1202) in parallel while adheringto a write latency requirement, determining the amount of I/O requeststhat may be processed by the storage system (1202) in parallel whileadhering to an IOPS requirement, or determining the amount of I/Orequests that may be processed by the storage system (1202) in parallelwhile adhering to other requirements. In such an example, one or more ofsuch performance criteria may be taken into consideration whendetermining an amount of I/O requests that may be processed by thestorage system (1202) in parallel while adhering to a performancerequirement.

The example method depicted in FIG. 14 also includes establishing(1404), in dependence upon the amount of I/O requests that may beprocessed by the storage system (1202) in parallel, the time-independentperiod. Establishing (1404), in dependence upon the amount of I/Orequests that may be processed by the storage system (1202) in parallel,the time-independent period may be carried out by establishing atime-independent period that includes one or more generations of I/Orequests. In such an example, each generation of I/O requests may beequal to the amount of I/O requests that the storage system (1202) mayprocess in parallel. Consider the example described above in which thestorage system (1202) can execute 1000 units of I/O requests in parallelwhile meeting a predetermined performance threshold. In such an example,a first generation of I/O requests may be defined as the first 1000units of I/O requests executed by the storage system (1202), a secondgeneration of I/O requests may be defined as the second 1000 units ofI/O requests executed by the storage system (1202), and so on. Readerswill appreciate that one or more generations of I/O requests is atime-independent period, as a generation of I/O requests may only covera small period of time when the storage system (1202) is receiving arelatively large number of I/O requests while another generation of I/Orequests may cover a much larger period of time when the storage system(1202) is receiving a relatively small number of I/O requests. In theexample method depicted in FIG. 9 , the time-independent period caninclude an amount of most recently processed I/O requests that is afunction of the amount of I/O requests that may be processed by thestorage system (1202) in parallel as the time-independent period caninclude an amount of most recently processed I/O requests that is equalto an integer multiple of the amount of I/O requests that may beprocessed by the storage system in parallel, the time-independent periodcan include an amount of most recently processed I/O requests that isequal to an fractional portion of the amount of I/O requests that may beprocessed by the storage system in parallel, and so on.

The example method depicted in FIG. 14 also includes determining (1406),in dependence upon the amount of I/O requests that may be processed bythe storage system (1202) in parallel, a weighted share of systemresources for each entity. Determining (1406) a weighted share of systemresources for each entity in dependence upon the amount of I/O requeststhat may be processed by the storage system (1202) in parallel may becarried out, for example, by determining how many entities are activelyassociated with incoming I/O requests and dividing the amount of I/Orequests that may be processed by the storage system (1202) in parallelin accordance with the respective weighted proportion of systemresources designated for use by each entity. Readers will appreciatethat although FIG. 14 describes determining (1406) a weighted share ofsystem resources for each entity in dependence upon the amount of I/Orequests that may be processed by the storage system (1202) in parallel,the weighted share of system resources for each entity may be determined(1406) in dependence upon the amount of I/O requests that may beprocessed by the storage system (1202) in parallel while adhering to oneor more performance criteria.

Readers will appreciate that although the many of the examples depictedin the Figures described above relate to various embodiments of thepresent disclosure, other embodiments are well within the scope of thepresent disclosure. In particular, steps depicted in one figure may becombined with steps depicted in other figures to create permutations ofthe embodiments expressly called out in the figures. Readers willfurther appreciate that although the example methods described above aredepicted in a way where a series of steps occurs in a particular order,no particular ordering of the steps is required unless explicitlystated. Example embodiments of the present disclosure are describedlargely in the context of a fully functional computer system forensuring the appropriate utilization of system resources using weightedworkload based, time-independent scheduling. Readers of skill in the artwill recognize, however, that the present disclosure also may beembodied in a computer program product disposed upon computer readablestorage media for use with any suitable data processing system. Suchcomputer readable storage media may be any storage medium formachine-readable information, including magnetic media, optical media,or other suitable media. Examples of such media include magnetic disksin hard drives or diskettes, compact disks for optical drives, magnetictape, and others as will occur to those of skill in the art. Personsskilled in the art will immediately recognize that any computer systemhaving suitable programming means will be capable of executing the stepsof the method of the disclosure as embodied in a computer programproduct. Persons skilled in the art will recognize also that, althoughsome of the example embodiments described in this specification areoriented to software installed and executing on computer hardware,nevertheless, alternative embodiments implemented as firmware or ashardware are well within the scope of the present disclosure.

The present disclosure may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent disclosure.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present disclosure may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present disclosure.

Aspects of the present disclosure are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of thedisclosure. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present disclosure. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

Readers will appreciate that the steps described herein may be carriedout in a variety of ways and that no particular ordering is required. Itwill be further understood from the foregoing description thatmodifications and changes may be made in various embodiments of thepresent disclosure without departing from its true spirit. Thedescriptions in this specification are for purposes of illustration onlyand are not to be construed in a limiting sense. The scope of thepresent disclosure is limited only by the language of the followingclaims.

What is claimed is:
 1. A method comprising: detecting that an amount ofsystem resources required to service a queued I/O request is greaterthan an amount of available system resources in a storage system;detecting that additional system resources in the storage system havebecome available; and issuing an I/O request from a queue for an entitythat has a highest priority among entities with non-empty queues,wherein a priority for each entity that utilizes the storage system isdetermined based on an amount of I/O requests associated with the entityin a time-independent period of I/O requests and a weighted proportionof system resources designated for use by the entity.
 2. The method ofclaim 1, further comprising determining a priority for each entity witha non-empty queue.
 3. The method of claim 2, wherein determining thepriority for each entity with a non-empty queue further comprises:determining an amount of I/O requests that may be processed by thestorage system in parallel; establishing, in dependence upon the amountof I/O requests that may be processed by the storage system in parallel,the time-independent period; determining an amount of I/O requestsprocessed for each entity with a non-empty queue during thetime-independent period; and assigning priorities to each entity with anon-empty queue in dependence upon the amount of I/O requests processedfor each entity with a non-empty queue during the time-independentperiod and the weighted proportion of system resources designated foruse by the entity.
 4. The method of claim 2, wherein determining thepriority for each entity with a non-empty queue further comprises:determining, in dependence upon the amount of I/O requests that may beprocessed by the storage system in parallel, a weighted share of systemresources for each entity; and assigning priorities to each entity witha non-empty queue in dependence upon the amount I/O requests processedfor each entity during the time-independent period in excess of theweighted share of system resources for each entity.
 5. The method ofclaim 1, wherein the time-independent period includes an amount of mostrecently processed I/O requests that is equal to a multiple of theamount of I/O requests that may be processed by the storage system inparallel.
 6. The method of claim 5, wherein determining an amount of I/Orequests that may be processed by the storage system in parallel furthercomprises determining the amount of I/O requests that may be processedby the storage system in parallel while adhering to a response timerequirement.
 7. The method of claim 1, wherein the time-independentperiod of I/O requests is a generation of I/O requests equal to theamount of I/O requests that the storage system executes in parallelwhile meeting a predetermined performance threshold.
 8. The method ofclaim 1 further comprising: determining the amount of system resourcesrequired to service the I/O request; and determining the amount ofavailable system resources in the storage system.
 9. The method of claim1, wherein the weighted proportion of system resources designated foruse by the entity is a fractional proportion of the system resources.10. The method of claim 1 further comprising, responsive to issuing theI/O request, debiting a resource utilization balance for the entityassociated with the I/O request.
 11. An apparatus including a computermemory and a computer processor, the computer memory including computerprogram instructions that, when executed by the computer processor,cause the apparatus to carry out the steps of: detecting that an amountof system resources required to service a queued I/O request is greaterthan an amount of available system resources in a storage system;detecting that additional system resources in the storage system havebecome available; and issuing an I/O request from a queue for an entitythat has a highest priority among entities with non-empty queues,wherein a priority for each entity that utilizes the storage system isdetermined based on an amount of I/O requests associated with the entityin a time-independent period of I/O requests and a weighted proportionof system resources designated for use by the entity.
 12. The apparatusof claim 11 further comprising computer program instructions that, whenexecuted by the computer processor, cause the apparatus to carry out thestep of determining a priority for each entity with a non-empty queue.13. The apparatus of claim 12, wherein determining the priority for eachentity with a non-empty queue further comprises: determining an amountof I/O requests that may be processed by the storage system in parallel;establishing, in dependence upon the amount of I/O requests that may beprocessed by the storage system in parallel, the time-independentperiod; determining an amount of I/O requests processed for each entitywith a non-empty queue during the time-independent period; and assigningpriorities to each entity with a non-empty queue in dependence upon theamount of I/O requests processed for each entity with a non-empty queueduring the time-independent period and the weighted proportion of systemresources designated for use by the entity.
 14. The apparatus of claim12, wherein determining the priority for each entity with a non-emptyqueue further comprises: determining, in dependence upon the amount ofI/O requests that may be processed by the storage system in parallel, aweighted share of system resources for each entity; and assigningpriorities to each entity with a non-empty queue in dependence upon theamount I/O requests processed for each entity during thetime-independent period in excess of the weighted share of systemresources for each entity.
 15. The apparatus of claim 11, wherein thetime-independent period includes an amount of most recently processedI/O requests that is equal to a multiple of the amount of I/O requeststhat may be processed by the storage system in parallel.
 16. Theapparatus of claim 15, wherein determining an amount of I/O requeststhat may be processed by the storage system in parallel furthercomprises determining the amount of I/O requests that may be processedby the storage system in parallel while adhering to a response timerequirement.
 17. The apparatus of claim 11, wherein the time-independentperiod of I/O requests is a generation of I/O requests equal to theamount of I/O requests that the storage system executes in parallelwhile meeting a predetermined performance threshold.
 18. The apparatusof claim 11 further comprising computer program instructions that, whenexecuted by the computer processor, cause the apparatus to carry out thesteps of: determining the amount of system resources required to servicethe I/O request; and determining the amount of available systemresources in the storage system.
 19. The apparatus of claim 11, whereinthe weighted proportion of system resources designated for use by theentity is a fractional proportion of the system resources.
 20. Theapparatus of claim 11 further comprising computer program instructionsthat, when executed by the computer processor, cause the apparatus tocarry out the step of, responsive to issuing the I/O request, debiting aresource utilization balance for the entity associated with the I/Orequest.